Would a MALE UAV with a dedicated ISR payload i.e. radars, radar warning receivers, TV cameras, etc. be all that vulnerable to SAMs at the edge of hostile airspace?
Sure UAVs with more longer ranged sensor payloads and longer ranged weapons (that can operate outside of the engagement envelope of enemy SAMs) would be more capable and more survivable if they can operate at standoff range, yes.
But the sort of sensor suite you describe is more consistent with what's present on a HALE UAVs than most MALE UAVs.
MALE UAVs typically rely on a primary EO/IR payload with a small radar at best, and usually need to be within 100km of the target they are surveiling -- more often within 50km of the target if they want more useful ISR.
If they want to do a strike mission, given most MALE UAVs use ATGM sized weapons like Hellfire or KD-9/10 with a range of well under 20km, that places the UAV at even greater risk just to get close to the target as they would have to venture through surveiled and defended airspace, as an aircraft that is kinematically defense less and without any meaningful signature reduction.
Doing that without extensive preceding SEAD/DEAD and ongoing supportive EW, is just a way to lose your drone.
And with the correct payload i.e. a radar warning receiver, even if the drone gets shot down you can get location data on SAM sites and launch a fast response munition like SRBM to hit the SAM site. Trading a drone + SRBM for a SAM site isn't that bad especially if you have tons of SRBMs.
Technically true, but that would be an expensive way to do SEAD/DEAD.
Better just to not risk your MALE UAVs in an environment where semi capable enemy SAMs exist and do SEAD/DEAD with more dedicated platforms first, before sending in MALE UAVs with EW support.
There's no reason to force MALE UAVs into a combat environment that they are inappropriate for, unless you have no other options, or unless you are a nation so rich that you can afford to toss away MALE UAVs in useless missions that other platforms can with better efficacy. But not even the US has that kind of money.
Russia might be able to make some use of WL-2 if they employ them carefully, but even against Ukraine's antiquated air defenses, it would be considered a vulnerable asset when in the air.