I'm speaking from experience!
It certainly doesnt support Solaris, I was unable to compile and install Gentoo, I also had a myriad of issues will memory allocations in various distros (I think SUSE 9.1, Slackware and Damn Small Linux off the top of my head).
Admittedly its at least 6-9months since I last tried VPC, but that is because everything has been so hassle-free with VMWare no matter what I am installing.
So maybe I am wrong and if so then great... but there are still a lot of extra features such as teaming and snapshot cloning that I couldnt now be without in VMWare that (as far as I am aware) are not possible in VPC.