Yeah, I also thought of the "guv'nor" thing! It's frustrating that Wodehouse was never more explicit about these things in his writing. Honestly, I think that would add a really interesting dimension to Jeeves's character.

I've always thought of him as having a very polished Received Pronunciation sort of accent (which is certainly the approach Stephen Fry went with), but I suppose there's no reason to assume anything about his accent from the way his speech is written.