I'm currently running it on VMWare ESXi server. I am having trouble with languages (english and japanese) on my server, but I don't think it's related to being virtualised. If I use an all English setup I can run Filemaker Server 11 Advanced on VMWare Virtual Machine with no trouble, including IWP. I have not had any strange crashes in the limited testing I've done. I can let you know in the future when I've been running it live for a longer time.
I can confrim that even though untested, FileMaker Server will run on a virtualized machine. I've used VMWare and VirutalBox and has worked with both.