The VM companies don's support non-Server Snow Leopard VMs, that's true. But what isn't true is that they don't support it because of the end user license agreement. There's no restriction in the non-Server Snow Leopard against installing it in a virtual machine. There is some other reason they don't support it. It's obvious to me that Apple made that a condition when licensing them the boot ROM code. Apple didn't want non-Server virtual machines, but since they didn't include such a prohibition in the end user license agreement, getting the middleman to block it was a way to achieve the same effect.
The VM companies aren't in the business of enforcing end user license agreements. Those are between Apple and the end users, not them. If the VM companies were in that business, they would block 10.7, 10.8, and 10.9 installations on host Macs running 10.10. Those are all license violations but the VM companies don't block those, because like I said, that's not the business they are in.
Anyway, it's all a moot point now since the fully supported SL Server only costs $20. It was a much bigger point of interest when it was $500 and cost-prohibitive enough to make non-Server SL virtual machines worth pursuing.