We have had great success with running FileMaker Server on virtualized OS X Server installations using Parallels Server.
We do also provide hosting on such, as well as on dedicated hardware servers. Contact me at jmay(at)pointinspace.com for more details if you're interested.
We use Citrix and VMWare internally. Although I havent put version 7 on either for the most part besides some small inuendoes it works fine for us with version 9.