Justin - although VDR itself has a similar frontend/backend client/server architecture to Myth, in the current LMCE implementation it doesn't support that, so you can only have VDR and your TV card on your core. You can't view TV on your MDs.
That said, 1) there is a hack out there that totallymaxed and niteman have talked about that will allow you to do this in a limited way. And 2) totallymaxed's company has just put out a revision that will go into 0810 that implements this (among much other stuff), so you can either way, or try tackling compiling the new revision of VDR they checked into the trunk (or perhaps 0810, not sure which).
I have Pm'd niz23 as he has some instructions on this. He is in Sweden (I think) so he has just got back to me with some pre-compiled binaries and instructions he is going to wiki-ise. I told him I would point you to him - either pm him directly or let me know if you want me to pass the binaries on to you myself (haven't downloaded and looked at them yet, so not sure what is involved)