If you're using one of VMWare's products, you do have to get a new activation code (as you found out), but once that's done the software should be fine from that point on, even in case of failover switching of servers. HyperV should also be fine.

If you are using a different type of VM environment, however, then I can't say for sure as we haven't tested them: you will have to experiment.
Technical Product Manager
I don't want to achieve immortality through my work; I want to achieve immortality through not dying - Woody Allen