It's confirmed that the OnLive version of Ravaged will have cross platform multiplayer
Source: http://www.2dawn.com/forum/onlive/7316-any-information-on-onlive-pc-players-mp#9041
If you have yet to check out Ravaged, you can watch he trailer here...
http://www.youtube.com/watch?v=R7qpkQxE0rA
The OnLive version is currently available for "pre order" at the price of $19.99