I'm a vim+qwerty user (I've tried learning dvorak, but it turns out typing speed is not my rate limiting factor and I don't have RSI issues). Only the hjkl cursor movement keys in vi(m) are position dependent, everything else is mnemonic. I see on the Colemak layout, that h/l are vaguely left/right, but j/k are down/up. Nevertheless, I doubt that would be a significant stumbling block. You could either use the arrow keys instead, or continue to use hjkl and deal with the funny positions.
I wouldn't be inclined to try to remap the vim functions depending on the keyboard layout. That seems like too much potential confusion for me.
