I was testing out the new features in 10.8 that allow NPEs to be used for OData Actions. However, it seems that if you're using NPEs with 0 capabilities checked (which is expected with NPEs), associations are not exposeable. This reduces the usability of the solution as it requires the implementer to flatten all of the NPE structures (or duplicate them) to utilize actions.
Hi Ryan, OData actions with nested parameters (using associations) is on the roadmap.