I wasn't aware of different wmv flavors.
Testing is really slow, because MCEBuddy has a LOT of options (which is a good thing in itself) and I don't have the Windows RT device myself. I can only wait until my friend has time for another test. That combined with the fact that I don't know anyone living close to me with a Windows RT tablet makes it a lengthy matter.
I am testing this, because I am still deciding whether or not to buy a Windows RT tablet. But I am pretty confident there MUST be some format that MCEBuddy can create of a .wtv file that IS supported by Windows RT.
As soon as I know more, I'll let you know!