Well, if you have the lenses, I would give it a try. The real problem is focus : since they are not coupled, only distance guessing or a rangefinder on the accessory shoe can be used. Was thinking about the same, but not with Leica-R, but Zeiss C/Y since I got a Bessa R2 and only have the CV90 for it right now, but would like to get the 28mm 2.0 Zeiss on this one for now. I paid for mine 370EUR and a new Ultron is selling for more around here ( new, that is ) and I would be surprised if it would be better than the Zeiss. Of course, it is larger/heavyer than the Ultron being 530g opposed to the 244g of the Ultron and 76mm to 51mm length, so you loose the size advantage, esp. since the adapter will add further length to the construction.
For my taste, even if I am a beginner in rangefinder/M land, there are little bargains out there. Even the best mid-long teles in R-mount start looking like bargains when compared to M-lenses on the used market. So life looks expensive in M-land, and the VC lenses are not that plentyfull on the used market so that you could net a bargain there either ( maybe with some exceptions ).
Regards,
Stefan