Has there ever been a case when a traitorous military commander took command again for the side he betrayed?

There was a near-miss in US history. In 1873, the Spanish navy captured an American vessel, the Virginius, that was transporting Cuban insurgents, and executed 53 Americans found aboard. During the standoff that followed, former Confederate general Nathan Bedford Forrest volunteered to lead an expedition against Spanish positions in the Caribbean. President Grant was considering the offer when the Spanish government apologized and the crisis was resolved.

(Whether Forrest, or Wheeler in another answer, counts as a traitor is obviously a highly contentious point, but cases like these may inform your understanding.)

Many participants in Rákóczi's War of Independence.

If you include "rebels" in the definition (one side's traitor is another side's freedom fighter), the officers who sided with the independence movement were defecting from their positions as officers in the imperial army. The reason for this was that Hungary was formerly split between the Ottoman Empire and the Habsburg Empire, the remainder forming a mostly independent Principality of Transylvania. After the end of the Great Turkish War, all of the above three territories ended up under the control of the Habsburg Empire. Francis II Rákóczi, prince of Transylvania, rebelled against the emperor and wanted to liberate all of Hungary from Habsburg control. Obviously, most of the military under his command fought previously in the Ottoman wars under the Habsburg banner.

As the war dragged on for 8 years, the Habsburgs offered many rebel generals their old positions and lands back if they switched back to their side. Some accepted, most notably Ocskay László. He fits the question the most, because he betrayed the emperor to join the rebels, and then betrayed the rebels to join the emperor again. Interestingly, after a series of failures in the emperor's employement, he was captured and was ready to betray the emperor again, but this time the rebels didn't believe him and, executed him. Another interesting example is Károlyi Sándor, another former imperial commander who joined the independence movement. Near the end of the war, Rákóczi gave him command over all the military with the order to continue fighting, but after evaluating the situation, he has seen more fit to arrange for a very forgiving peace treaty instead.

After the war ended peacefully with the treaty of Szatmár, the rebels were granted full amnesty, and many military officers resumed their duties in the emperor's army.

Marshall Conde of France took part in the "Fronde" insurrection in France, in the mid-17th century. He (and his sister) were "excused" because they were upholding the sister's husband, not in their own right. According to Wikipedia:

"She, [the sister] alone among the nobles who took part in the folly of the Fronde, earned respect and sympathy. Faithful to a faithless husband, she came forth from the retirement to which he had condemned her to fight for his freedom."

He was taken back by Louis XIV and served faithfully thereafter. even though the Fronde had been "flirting" with Spain, a foreign power.

Lü Bu (Eastern Han dynasty) was pretty famous for switching sides. I'm oversimplifying, but:

189: Served under Dong Zhuo, capturing the capital of China. Promoted to general.

192: Helps assassinate Dong Zhuo. Goes to Yuan Shu (though rejected).

194: Commanded soldiers under Yuan Shao. Yuan Shao tries to assassinate him. Join's Zhang Miao's successful rebellion against Cao Cao.

196: Defeated by Cao Cao, and sheltered by Liu Bei. Recruited by Yuan Shu to betray Liu Bei, which he does successfully.

197: Betrays Yuan Shu.

198: Joins Yuan Shu again, to fight Liu Bei. Captures land from Liu Bei for Yuan Shu.

198-199: Besieged by Cao Cao. Captured by Cao Cao and executed.

His service under Yuan Shu is an example of a traitor being given command again, when his treachery is well-known.

I would suggest Thorkell the Tall, a Viking commander who attacked England in 1010 for the Danish King Sweyn Forkbeard. His army, for instance, laid siege to Canterbury, took the city, and burned its cathedral.

In 1013, Thorkell and his army defected and fought for King Æthelred against Sweyn and his son Cnut, keeping him in check during the siege of London. After Sweyn's death, Æthelred's forces turned against every Viking in England and Thorkell went back to Cnut and fought for him again in the conquest of England in 1017. After their victory, Cnut gave control of East Anglia to Thorkell.

In the end, he fell out (again) with Cnut, but that's another story.

It seems that Thorkell and the legendary Jomsvikings were very valuable and that Thorkell taught King Cnut how to fight and this is why Cnut accepted his allegiance again.

If you define "traitorous" as "rebelling against a country you once served", then there's Joseph Wheeler who served in the US military, went to fight against the US military as a Confederate officer, then later fought for the US military in the Spanish American war.

There are many in the US who take great exception to the idea that Confederate soldiers were "traitors", though.

(1) Alcibiades, of course.

During the course of the Peloponnesian War, Alcibiades changed his political allegiance several times. In his native Athens in the early 410s BC, he advocated an aggressive foreign policy and was a prominent proponent of the Sicilian Expedition, but he fled to Sparta after his political enemies brought charges of sacrilege against him. In Sparta, he served as a strategic adviser, proposing or supervising several major campaigns against Athens. In Sparta too, however, Alcibiades soon made powerful enemies and felt forced to defect to Persia. There he served as an adviser to the satrap Tissaphernes until his Athenian political allies brought about his recall. He then served as an Athenian general [...] for several years [...]

(2) George, Duke of Clarence almost fits - but maybe not quite. He sure switched sides twice but he was not given a military command upon re-defection - perhaps because there was no war going on. Had there been one, I presume he would have commanded part of Edward's army.

(3) Vladimir Gil (Rodionov). He was a lieutenant colonel in the Red Army. Early in the German invasion of the Soviet Union he was captured by the Wehrmacht and joined the German side.

He quickly rose in prominence in the German service and was able to create his own SS "eastern legion"-type unit, which was eventually known as the 1-я русская национальная бригада СС «Дружина» (1st Russian National SS Brigade Druzhina).

Then, in August 1943, after some clandestine negotiation with the partisans he had been fighting so far, Gil defected back to the Soviet side with his entire unit (killing the German officers attached to it in the process), which was now promptly renamed as «1-я Антифашистская партизанская бригада» (1st Antifascist Partisan Brigade). Gil remained in command, retained his rank, and was even awarded the Order of the Red Banner.

He died of wounds sustained in action in 1944, so we cannot tell how his fate would have played out post-war but I doubt he would have been able to weasel his way out of a court-martial and possible execution. As long as the war lasted, though, he was useful to the Soviet command.