In an emergency I would hope that FEMA would have some say (or at least coordination with the FAA) over what aircraft is in the sky over the affected area.
FEMA would ask the FAA, and the FAA would create a TFR* or similar as appropriate. Enforcement would be entirely up to the FAA, as it's their thing.
* Temporary Flight Restriction, a small area restricted for general flight in order to ensure clear airspace for disaster recovery, firefighting, or certain high-profile VIPs (e.g. Air Force One gets a TFR around it).
FEMA is supposed to coordinate to aid disaster preperation, response, and recovery. They have wide ranging powers to do so because there are a wide range of disasters out there.
Suppose you have 20,000+ stranded on a tiny island in the middle of a flood. Your air lifting in supplies but there are several news helicopters in the area slowing things down. You can't tell them to go pound sand directly but you can call the FAA and get the FAA to tell them to GTFO.
The smart manager delegates. Same in disaster response as in a dev shop.
I would rather the FAA, who do it day in and out and have response and contingency plans for every eventuality, be in control of the airspace than an agency with no regular practice.
Give unto agencies, that which is in the domain of those agencies. FEMA gives the directions for them to follow.
If the FAA says that the drone can fly in those conditions, they can fly in those conditions.
Although, recently, it looks like the FAA grounded the drone.
Regardless, it isn't the role of FEMA to tell airplanes that they can't fly. That's insane.