If there is a reason to do it, then it's cool. But it's very easy to abuse the fish eye lens. There has to be a reason. If you're doing it just to do it, that's where it can become gimmicky. We feel that a fish eye works well if you want to get an overall shot of the venue or all of the guests. It's also fun to use if you want to get a silly shot. For example, a dog wearing a tuxedo close up, or a goofy shot of the groomsmen. But it's not a flattering lens where a bride will say "Wow, I look amazing!"
We feel that using a fish eye lens more than two or three times in a wedding is pushing it. There are other ways to be creative.