Hardly suicide. Lol at this thread. I've tested gengar extensively, and unless they run palkia you should be good (even with it you still have a chance). Keep in mind gengar hasn't been perfected, and I know allot of people are forgoing the devoluter in order to make room for other techs. Assuming they have both, then even then you still have a chance.
Keep in mind if you hit a fast gyarados they aren't going to be able to compete with it for at least one turn, meaning you you can probably grab at least two prizes, if not three with the first gyardos (remember it takes them two attacks to kill your gdos, even with the TM, and you're probably going to KO a starter before that).
A belt and two bat drops is probably not asking too much from gdos, so the odds of one shotting a gengar isn't all that unlikely. Keep in mind too, if you run the dialga g lv. x tech then their they also need to level you down, and that's assuming you didn't drop a mesprit.
I'm not saying it's an autowin, but gdos can definitely pull it off, and since most good players have already put cyrus in their build to deal with the primes that are in vilegar, they don't have to worry about lost karps from collector. Worse comes to worse, gdos can play dark energy, and a good dark type tech if they REALLY had to, but in all honesty I think that would hurt you more than help, even against lostgar.
EDIT - Politoad is right, mew would be an excellent tech, great idea.