Yes, it seems indeed adjusted by the enemy stats option unter difficulties.
I don't remember whether Pathfinder actually juggled with enemy DR on those settings. It may make sense though given the scenario (and demons usually having DR it seems).
The problem I still had, playing on "normal" pre-sets so far as said, but with enemy damage increased to 100%: Unlike the reduced AC (-2) say, the game doesn't show anywhere that the DR IS actually being adjusted. Hovering over a dretch demon, say, it says there'd be a DR of 5 (accordingly to the P&P stats) regardless what difficulty you pick.
There's another problem I have: I',m not a huge fan of "stat bloat", which Owlcat seem to apply in particular on higher settings. Huge ACs, you name it.
I wish there was setting solely for enemy DR, but the enemy stat adjustments alters everything, not merely DR.
