The way this question is worded suggests potential problems because you want to know if your independent contractors can be employees and even though a business is free to engage independant contractors and/or they can have employess; you will start to get into trouble if you regard the same person as both! Here is the IRS guidelines self-employement vs employment. In you're case, it would certainly depend on things like:

* are your contractors free to decline shifts that you offer or are you really expecting them to do whatever you want?
* do your contractors have other customers besides you?
* do they bring some aquired skill set (nursing?) or equipment that they own to the gig?
* do their contracts begin and end or are they really perpetual and ongoing, from one contract to the next.
* are they free to sub contract the work out to other people or are you really expecting them, and only them, to do the work.

A worst case would be that after a few years of doing business with your "independant contractors" is that you might be liable for employment taxes if they claim that they were really more like employees.