The simple answer to your question is yes, in many places Endo RN's are administering anesthesia. The fact is that any time you give propofol IV push to a non-intubated patient, you are administering anesthesiia. And if you are an RN who is not a CRNA, you are not qualified to do so, disclaimers about "annual competencies" and "ACLS certification" not withstanding. These RN's are taking an enormous risk with their licences, with their liability, and worst of all, with their patients' lives.
So, why are they doing so? In the end, it isn't about patient comfort (though that may be the nurse's goal), nor is it about saving the patient money. It is about maximizing the profit for the GI doc, period. If he or she can convince the RN that they can safely give an anesthetic, they can charge for the sedation as well as for the procedure. Worse, I've never yet met a GI doc who was competent to administer an anesthetic, so if there is a severe problem, the doc won't have the slightest idea what to do. Leaving the RN, and worse, the patient, swinging in the breeze.