Are there any Trinitarian denominations that do not view belief in the Trinity as a "salvation issue"?

Your phrase, "belief in the Trinity as a 'salvation issue'" is problematic. The question would be clear if it was about the Athanasian Creed making belief in the trinity a 'requirement for salvation'. That would be one thing. It is another thing entirely to ask whether today's thousands of mainstream Christian denominations that do believe in the triune God, consider belief in that to be a salvation issue. Because that is another thing. The need would then be to explain how a 'salvation issue' becomes a salvation 'requirement', for those are distinct matters, even if closely connected.

The Bible is clear as to what God requires for sinners to receive his salvation and, as we all know, the word 'trinity' does not crop up anywhere there. Yet in both old and new covenants, faith is the essential element. Of course, that faith has to be in the one true God, who alone is to be worshipped. That is why the O.T. has examples of such shining, saving faith in the likes of Abraham and Moses, who are detailed in the N.T. as those who saw by faith, from afar, the heavenly 'country' they sought (Hebrews 11:8-10 & 23-27). Once Christ came into the world, then died as the essential perfect sacrifice in the plan of salvation, the new covenant came into force. As Hebrews explains, the death of the testator has to happen before his testament comes into effect. The new testament in Christ's shed blood then made clear how salvation was achieved for the many, at Golgotha and the empty tomb. Then Hebrews was able to show how superior the risen Christ is to any created angels and to the old covenant system. The immensity of just who the Son of God is was unfolded in the N.T.

Faith in THAT Christ is essential for salvation. The Bible rules out faith in other gods, in false prophets, in false Christs, in false systems of salvation by works, in false 'doctrines of men' which Jesus Christ castigated religious leaders for teaching (Matthew 15:9 quoting Isaiah 29:13). This is where the close connection between having faith in the biblical Christ as a salvation requirement is seen. Should any professed Christian claim to have faith in a Christ who is not the Christ of scripture, then that person would not have faith that saves. To have faith in a man-made concept of who Christ is would actually debar a person from salvation as that would be the greatest insult to the Lord's anointed Christ. That is why there are such strong claims and counter-claims made about mainstream Christian teaching that the Son of God is the uncreated Word of God who both was with God in the beginning, and who is God, and who made everything that was made (John 1:1-14). Trinitarian belief is founded on such biblical revelation (and a whole lot more), while denominations that are not trinitarian don't sit on the fence with this issue, but roundly condemn trinitarianism as false religion.

In the era of Athanasius, there were vehement attacks on the doctrine of the person of Christ. To protect the Church from teaching that would undermine the person of Christ, and thus annul the whole event of salvation achieved by him, anathemas were added. Those who said there was "a time when Christ was not" were cursed. The Church viewed those who said Jesus was a created creature as heretics (which certainly made that a 'salvation issue'!) The same situation obtains today. There are still those who say God created Jesus at a certain point in time. Trinitarian denominations warn that anyone teaching that is actually teaching heresy and leading people away from God's salvation in Christ, because they are following man-made teachings about who Jesus really is - a false Christ, in other words. However, many people who once believed that Jesus had been created have later come to saving faith in an uncreated Christ, in Jesus as God incarnate. This means that it is possible to so grow in understanding and faith in Christ that the 'salvation issue' about who Christ is, is resolved. Just keep in mind that Athanasius was concerned to expose heretical teaching that threatened the Church. Teachers of heresy do not meet God's requirements for salvation, and they are, indeed, accursed.

There is no trinitarian denomination that does not view belief about Christ being uncreated as 'optional' regarding salvation. But please don't confuse that with putting the Athanasian Creed on a par with the Bible, and Jesus' own words about salvation. Nor does this matter of salvation require each person who becomes a Christian having to clearly explain this - the deepest of doctrines - in theological terms. The basic requirements for salvation call for repentance of sins and faith in the finished work of Christ - to believingly call upon the name of Christ to be saved. As a new Christian grows in understanding, they will then come to grasp more about the Christ who saved them. Just see the Athanasian Creed as a necessary mile-stone in Church history for protecting against heresy; nobody's salvation depends on upholding its every word, for it was written to clarify various Christian beliefs that were becoming muddied due to heresies back then. Everything anyone needs for salvation is to be found in the pages of the Bible, rejection of which disqualifies one from salvation. Those who understand the deep things of God contained in the Bible will understand why the Athanasian Creed was so written, with its anathemas against teachers of heresy.