I think the line between bellydance and something else is very difficult to draw. For example tribal dance is very different from Egyptian style bellydance but personally I think it can still be called bellydancing due to the movement and general feel it has.
I have seen "fusion bellydance" where the dancer dances to techno music, wearing the kind of dress you would expect to see people wearing when they go out to party at a club, and her dance had a lot of elements from something like show dancing etc. The only thing about her show that was bellydance for me was a hip scarf and a few bellydanceish movements. I wouldn't call this bellydance.
However, I consider myself quite open-minded when it comes to mixing different styles and elements from different kinds of music, cultures etc. Bellydance has been changing all the time and adopting elements from other cultures, for example the two part bedlah we consider so classical doesn't have its origins in the Arab culture - but where to draw the line? When does it stop being bellydance and becomes something else?
I like to dance to music that is inspired by Scandinavian folk music. You can find interesting rhythm patterns and the kind of variation you often cannot find in western dance music - or, for that matter, new Arab pop. However the dance I'm dancing has nothing to do with Scandinavian folk dances (I don't even know anything about them even though I'm Finnish). Obviously the music affects the feel and style of the dance, but I'm only using bellydance moves. I consider this fusion bellydance but I understand some people may disagree.