You won't have GPU support or Firewire support, but everything else should work fine. I run Vegas Pro 11.0 on my Snow Leopard Mac with VMware Fusion. Parallels should work too.
Here is a screen cap from my Vegas Pro 10.0 running in Unity mode:
You may also want to check out the option of running Vegas on your Mac w/Bootcamp. I got rid of a lot of headaches when I ditched Parallels and set up a dual boot system. Better performance & stability (for me).