Deunan has released a Dreamcast VMU Emulator for Nintendo DS :
And so here it is. Be sure to go through the ReadMe file!
Unfortunately it turned out that VMS is a bit of a CPU hog, too much for the poor ARM9. In the end it's just another random piece of semi-useful homebrew Hard to say what exactly is the limiting factor here, I'm too lazy to do any serious profiling, but seeing how it's almost working I'd say some more MHz and/or cache would do the trick.