Those things use active radar themselves, or alternatively, follow a laser (presumably generally from the firing vehicle).
I’m not sure if the temporary radar pulse is going to make much difference.
Not really, but if the aircraft launching that Hellfire announces itself like that prior to firing, just to check who you are, it may give you just enough information to fire at it preemptively, or at least know (or let others know) where to look for it.
It's not a problem if the US is fighting a technologically inferior opponent, but apparently (from what I've read on HN the other day), the US military is retooling itself towards competition with China, so they have to consider their technological trickery being used against them.
I think this only works for the targeted party, which sends a pulse, which you could potentially triangulate on. The firing aircraft sends a very narrow beam of signal, so unless you have a specific setup to detect the direction of the signal, you’ll just know you were hit by an unidentified radio beam.
I’m not a radio expert though, who knows what I’m missing :)
Theoretically maybe still a problem if the enemy is waiting for that moment to shoot at you, but to wait for a friendly fire incident seems a bit inefficient.