How do I say 'fellow sweet tooth' (noun) in japanese. I'd thought it would be either 甘党仲間 or 甘党同僚 but there's probably something more accurate
The word "fellow" in English is often too casually used to find an all-around translation.
Moreover, in the provided context:
As a fellow sweet tooth, let's go to a cake buffet.
this fellow practically stands for "me, who am one of" and probably "me, like you guys". In this case, I don't think any literal-ish translation of "fellow" works.
Natural ways to express it would be:
甘党仲間 sounds somewhat not right in this context, because it's like talking about the third party, or from a distant view point. 同僚 is unusable at all, as it only means "colleague".