If they subcontract you should make sure they have their OWN insurance. I would talk to an attorney on this but I heard even with their own coverage, if they have a problem or get into trouble it can still bring you down... but again, I would talk to an attorney on that to be sure you cover yourself.
If they will be employee's you would provide the E/O making sure they are covered. You will also want to make sure all your HIPAA associate agreements are in order and you will need to disclose them on yours with your clients.