I'm not 100% certain, but I do think it would work. The two procs are closely related - the the Q6600 Kentsfield is basically made up of two E6750 Conroe procs and they have the same features - so I do think you'd be able to vmotion between the two.
If you did run into problems, you could always look at enhanced vmotion. The server class chips in the Conroe and Kentsfield families are listed in VMware's docs as being enhanced vmotion compatible. Your CPUs are desktop class processors but they still might be EVC compatible. I just can't say with any certainty as the documentation only references server class cpus.
