Well, I only know of resolvers from a Motion training class that I recently went to, and we only touched on the topic. But from my understading (and memory) there are two coils in the "resolver portion" and magnets on the rotor. When the shaft rotates, the magnets cause a sin wave on the two coils. The coils are offset 90deg to determine direction. The ouputs from the resolver just plug into the inputs of your drive/controller and it does the rest (same as encoders). Now you may have to use a more industrial drive to accept resolver inputs as they are completely different inputs then encoders. Those motors look more like "industrial grade" motors which is probably why they have resolvers.

And again, I am by no means an expert on resolvers.