Can you delegate RC that is delegated to you?

No

Also something interesting is that delegating RC requires only posting auth, so I envision a service where you can "lend" your RC, you give give posting auth to that service and it would do rc delegations on your behalf. I know I would be more than happy to lend my rc to help newcomers/dapps like peakd. Realistically a few dolphins or a whale could probably power tens of thousand of users