Yes. Well, I don't do trials very well, even on a trials bike. There are those that do, I've seen some people who can do amazing things in trials competitions on a mtn bike. There is no questions that a pure trials bike is better but still you can do a lot of the manuevers on any bike. Do a search for bicycle trials and you can come up with lots of good links.
In AR at some of the series mtn bike races they now do the xc event, a dh event, and a trials competition. I've never entered the trials but I always watch, it's a brutal sport and it amazes me what some of those people can do...