If RNG does use a seed, it should probably be randomly generated each time the game loads (md5 timestamp?), not tied to a fixed string.
I'm unsure how doing this would change much except in very specific and unusual circumstances. Randomly randomizing the randomizer should be nearly indistinguishable from a high-level fixed seed. Assume that the RNG seed is the same as the RWG seed. That is, when you generate a map, the RNG seed is set and every playthrough using that map will have the same starting RNG seed. And so let's say that BarrysWorld RWG seed always produces these first five RNG numbers:
0.27, 0.97, 0.12, 0.84, 0.77
It may be that in your first playthrough on BarrysWorld, those numbers don't produce results you like. You search two vehicles, a trash pile, a bookcase, and a medicine cabinet in that order and you get junk in your opinion. Extend from five RNG numbers to 1,000 or 10,000 and the idea is the same. Maybe it doesn't work out and you think the RNG is bad.
But if you start a 2nd playthrough on BarrysWorld, same RNG seed, and make even a
miniscule deviation in how you "used" those 5, or 1,000, or 10,000 RNG numbers, the experience would be completely different. Maybe you search the trash pile first and then the medicine cabinet. Well now 0.27 is used for the trash loot and 0.97 is used for the medicine cabinet (instead of two vehicles as in the 1st playthrough). Maybe the loot won't be much better, just different. And just as random even though the seed is identical.
There may be an instinct to treat RNG seed like we do RWG seeds. "Ooh, this seed has a nice city and 7 traders" becomes "Ooh this seed produces lots of beakers!", but the RNG doesn't work that way. The seed just determines the pseudo-random stack of numbers the game can use; they are used at run-time based on the actions of the player(s) in the game. Change the actions, change the results.
Edit to add: there's evidence that the game might use different RNG seeds for different things, too. POIs with random "helper" blocks (maybe it's a searchable cabinet, maybe it's an open/empty one) seem to get randomized at playthrough creation, if not RWG creation, and don't rely on run-time RNG checks like it used to in A19. That is, a quest location doesn't sprout new searchable cars or cabinets when you reset it like it used to. For random loot generation (which occurs when you search the container), it wouldn't matter. It'll appear random and be different between different playthroughs.