score:3
Machines from CTBC Bank accept Plus cards. There is one a few kilometers north of Hualien.
Unfortunately, there does not seem to be a generic solution for this. VISA, owners of Plus, has an online ATM Locator. According to it, there are only two Plus ATMs in Eastern Taiwan, one Hualien (Shin Kong Bank) and one in Yilan (Citibank). Being closer I took a 1h20m detour to Hualien, being sure that it would work. Unfortunately, it did not. In a bit of a panic, I headed north and hit every single ATM along highway 9. Finally, after 19 tries, I found one with the Plus logo and it was in a 7-11 (other 7-11 ones failed, so it depends on the ATM provider).
For completeness I also tried a Cirrus card at every point and none of them worked, despite being clearly aware this was a Cirrus card. I was prompted each time if I wanted to use Cirrus transaction and most machines eventually spit out the card before printing a receipt saying Transaction Failed.