Intriguing idea. I think maybe you're understating the prominence of Surakism on Vulcan, but every society has its dissidents and minority beliefs. We have seen Vulcan schismatists before (in "Gambit" and multiple novels). And it is indeed possible that some groups sharing V'Las's sympathies would've lived on.
So you might be onto something. Historically, successful conquest has almost always relied on co-opting indigenous talent to manage their own territory on your behalf. You go in, identify existing political rivalries, and help one group get the power/control/freedom from the current dictator/whatever that they crave, in exchange for which they send you tribute and follow your instructions. So they do the work of ruling the territory for you. It makes an empire far more manageable than if the metropolis had to stretch itself thin by directly regulating all its territories.