The first time through Lost in Nightmares, I didn't encounter a single enemy in the mansion. Nothing. However, both times since then, I have. Both times was after using the classic camera angles.
The first time I encountered an enemy was just after hitting the switch that keeps Jill from being (forgive me) made into a Jill sandwich. Immediately after leaving that room and entering the room with cages and junk piled up, I saw the new enemy's anchor weapon get dragged in the foreground of my camera view. So I gave chase and went into the hallway, and there he was trying to walk back towards the entrance hall.
On the playthrough after that, I was heading to the dining room with the fire-sensitive paper to get the last password. I decided to investigate the piano room since I heard music playing and because I had never gone back there before.
So I get to the piano room and there's nothing, and the music had stopped playing as I was going up the stairs. It was creepy, but I was disappointed. However, when I left the room and tried to go back downstairs I was attacked by another anchor-wielding enemy.
I'm not sure if those moments only happen if you use the old view or not. All three of my playthroughs have been on Normal, by the way. So difficulty has nothing to do with it. I jumped both times though, so it was pretty cool.