Is there a way to pull user usage data from the Valence API?
In particular I want to know if a user has ever logged in or accessed a certain course.
No, sorry, currently that information is not available through the Valence APIs. If you'd like the Valence APIs to provide that information, and you're affiliated with a D2L customer, please use their account management chain to report your request. If you're not directly affiliated with a D2L account manager, then you can report your request through the Valence support chain.
This particular request is something that other partners and customers have indicated an interest for.