As explained, ADS-B transmissions need not originate with the aircraft that is identified. If there is primary radar coverage an ADS-B transmission can be originated by ATC to represent the majority of factors that apply - location, speed, altitude, heading are enough to provide useful situational awareness. If they know any other information that also can be included.
ADS-B In alone is sufficient for drone operators to take active evasive actions to avoid manned aircraft which use ADS-B Out. There is no need for manned aircraft to be distracted by a swarm of drones that are easily able to fly in any direction, to the ground if required, to stay out of their way. There is the question of drones dodging each other and a need for that system, but not for the safety of manned aviation. This is why hobbyists are developing the tech, though in the USA the FAA refuses to ensure that manned operations do their part.
For emergency uses manned aviation could add drones of their own, with ADS-B Out and with ADS-B repeaters so that aircraft operating in areas where the signals are degraded by operating in irregular terrain could maintain adequate situational awareness while giving emergency and amateur drone operations the total picture they need.