<p>Site 1 has dll's for x amount of object and data calls.  Can Site 2 (a separate .net web app) call the objects/dll's of Site 1 ?</p>

This may be more semantics:
You can't call an object of another process.  You can however potentially instantiate a class within a dll as long as there is a reference to that dll in the calling web application.
If you GAC the dll, the classes (not objects) will be accessible to the entire machine.