All resolving will occur before any rendering (as you have to resolve everything in order to know *what* to render) and, yes, I believe that "Show Items to Publish" includes items resolved by custom resolvers.

So, essentially, publishing items explicitly at render time will always supersede any action taking during the "resolving" phase.

In your scenario, you exclude the Multimedia Component when resolving the items to publish but then publish it anyway when your templates are rendered.