I'm sorry but I must ask why was the FF V protagonist called Butz in the US? Was it the same in japan?
I'm pretty sure it's Bartz, unless you played the fan translated version of it for SNES, 'cause that one never made it to US shores.
Well, in the Dissidia website, I see his name, written in kana, as バッツ, which directly romanticized is Battsu. On the Dissidia website they also have their names in English atop the kana and it reads Butz.
Therefore, the "correct" spelling is Butz... But as with Cefca being the correct spelling for Kefka, I doubt many outside of Japan really like Cefca as the spelling... and Butz sounds like butts [insert immature jokes from people who just got it]... In the US, I remember seeing his name as Bartz.