I've always run SEM or SEPM on VMWare servers and earlier this year put the latest SEP/SEPM on Server 2008 R2 (64bit) and have had no issues that are a result of the VMWare.
It's smooth. I will say it takes some HP so configure accordingly or you'll find SEM wants more processor or memory than it's got.
I give it a large base configuration (4 gig RAM, 2 dual core processors), but it can "rob" from others when needed.
I know of others using it just fine on other virtual products with no issues.
I'm really glad you folks typing in ru6mp1 aren't missing the 6 in there...............