To address this question, quite a few factors have to be considered and I believe the answer is not as simple as a yes or no. Among the factors to consider are the location and availability of supplies that can treat the illness that are approved. In the field, during natural disasters, or in the event proper medical care will not arrive in time, the use of unapproved medical devices are permitted for first aid treatment. Instances of this can be seen in medical emergencies in airplanes or in disaster zones with limited/lacking equipment. The tube portion of a pen has been used as a medical device during first aid treatment of patients with certain lung diseases when approved devices are not available and the patients life is in danger.
see the guidelines below:
https://www.fda.gov/RegulatoryInformation/Guidances/ucm125127.htm

Currently, President Trump is trying to make unapproved treatments(from my understanding drugs mainly) available to patients with serious diseases who are left to either miraculously recover or live the remainder of their life waiting of a cure to be approved or dying. If that becomes law then we will see a new shift in the medical field. As to how that eventually impacts medical devices is yet to be known.
But with regards to the original question, within hospitals, it is highly unlikely for them to encounter a situation where unapproved devices can be used in emergency situations except in situations like in puerto rico.