Right you are! I wonder why 10.6 stuck in my head, I even got the first Xeon MP (as a free replacement from Apple for my G5 PowerMac liquid cooling blowing out and destroying my system utterly) in 2006 and it was Tiger. What a time since then. I guess 10.6 Server was the first officially virtualizable version so maybe that's why, but yes you're absolutely right, 10.4(.4) and 10.5 should both be runnable in a modified VM in principle.

Though I'd suggest its probably easier to run the PPC versions at this point.