I just want to remind everyone to remain on topic and to not deviate the discussion towards SW ep.3.
Back on topic,
To counter JediShemL's point that Vaklu states that he knows nothing of Jedi ways. Couldn't he just lie, after all in that scene Vaklu is trying to gain the PC's trust and help.
I think Master Dakari's Back story is a reasonable rationaliztion to Vaklu being Sith trained.
On the technical aspects editing Valku's appearance.2da row would be fairly simple all you need is the head and uniform. Then all that you would need to do is give Vaklu a lightsaber the feats to use it and some Force powers which could be scripted in.
I personally would find it a little strange to see a Dooku look alike, but thats just me
Then again its not much different than OE re-skinning Carths head for Vaklu.