@ovrarrest - depends WHICH rMBP you've got. If memory serves, only the ones with nVidia GPU can drive all 3 outputs at once - the regular IRIS only chipset rMBPs can only drive 2. (I could be wrong tho).
Yep, Vidock works on OSX with graphics cards, and their are single graphics cards out there that have up to 6x native outputs built in... therefore you could run 12x with 2 such cards in a ViDock - you just need to hunt further when it comes to the choice of graphics card.