Does RDP support Multitouch? (and if not, does anything?)

Yes, it does. Proof is that the Windows Simulator coupled with the new Visual Studio with Metro supports multi touch. It loopbacks an RDP connection to your Windows 8 system and allows you to use your mouse as finger and some gestures work too. It's for testing touch apps without the screen, by the way.

This does not seem to be plausible using RDP nor any other tool available. Usually multitouch support requires the OS to be installed on the hardware that is recognizing the gestures.

The same way that I can access an iPad or iPhone via VNC from my desktop, it does not support the multitouch from my desktop. It seems to be most likely that this does not work the other way around either, regardless of the tablet manufacturer.

The only way to have the functionality your are looking for, is to use the multi touch shortcuts that RDP, VNC etc have to offer (left click, right click, drag and drop, scroll wheel, zoom and change monitor functions).