It's a custom build, it contains the latest 0.20-release-fixes + a segfault preventing patch + keyremapping patch to avoid key collissions on F6-F8 + several patches from the ubuntu folks to allow it to work with the ubuntu file system layout and with the ivtv drivers in the kernel we're using + some patched to avoid nagging about missing ivtv ioctl (which are absent in the ivtv used by ubuntu).
As far as working with other non-LMCE MythTV installations on the same network, it is network and DB compatible with 0.20.1, 0.20.2 and pretty much all packaged 0.20.x versions (there was a bug in the initial 0.20.0 release, that required a network protocol change, but pretty much all major distros released a 0.20.0 with the fix).