In the end, EMC's (aka VMWare's) attorney's are much better at this than any of us. If something's not kosher, I have no doubt that Apple would have told VMWare, and Fusion would block it from happening (i.e. 10.7 on 10.8, etc).
The big thing for the OP is the need for server licenses for 10.6 and 10.5, as the client can't be virtualized - either by the EULA or by Fusion's technical limitations!