My docs always explained that it was hospital outpatient "just in case of a tear or perforation" - which would require pretty immediate surgery.
An endoscopy center is typically set up much like an ambulatory surgery center. Likewise, the center should have emergency plans for immediate hospital transport in the unlikely event a procedure becomes complicated. At this point, I couldn’t wouldn’t venture a guess about what contingency policies and procedures the Las Vegas quack shop had in place.
I've had colonoscopies at my gastroenterologist's office, however it's in a medical complex with a hospital attached, so in a worst case scenario, I suppose that a patient could be in the ER within a few minutes.