Versions support on a Samba share
The design of versions is very client Mac centric. 

The local Lion OS detects an app is calling document based API and enabled the versioned store in a space that is local to the Mac and different than the actual document. 

All version data is stored at /.DocumentRevisions-V100 and you can explore and test with simple documents in TextEdit to poke at the implementation artifacts. 

I suppose you could mount that directory to the server and experiment, but I don't see any locking or merge functionality and expect a world of hurt if two clients tried to share the same document and version chain simultaneously. 

Perhaps the engineering work will be done in the future to allow versions over Xsan storage, but it looks to me that the implementation is only for local versions.