I read in a previous thread that VCs sometimes do reference checks before signing a deal. That's fine, I work for one of the Big Co's in the valley and they can confirm my employment there.

However, do they typically have a verbal chat with the prior manager, like a fully-fledged job reference?

The reason I don't want to use my manager as a reference is because I've never done any overtime. Any spare minute I've ever had has gone towards a startup or side project.