LinuxMCE uses MythTV for it's backend TV recording. MythTV .20 supports UPnP. I haven't had a chance to try it with LinuxMCE but I can attest to it (MythTV .20) working very well without LinuxMCE. As a UPnP server for video, pics, and music it's great for any UPnP client.
The limitation in the media it serves is in your client, files are served in whatever format they're stored, so if the client can't read a *.nuv file, (TV Recording) then you won't be able to view it without some creative conversions to a more compatible file format. There's a few scripts available in the MythTV wiki to accomplish this, but "out of the box" it's not there.
If LinuxMCE doesn't already support the UPnP offered by the portions MythTV it uses, I don't think it would be a hard adoption of features. This would be your best bet.