My mod I'm currently working on.

[Hypercube]

You could add a collide area that just collides with everything, but then you'd run into issues because it collides with everything, including things you don't expect it to be colliding with. With keeping to neat organization and all around general sanity, it might be easier to just have two overlapping areas for the player and the monster each.

(Although, I think that most monsters have it built-in to their AI code that if a path node rests on top of a door, they will open the door themselves already.)

I see what your saying, and I kind of do think it would be better for it to collide with say every entity in my map, because it's supposed to be like motion sensor sort of things, and making two seperate areas for all of those doors in my mod would be a lot of stuff to script that I don't need. And if the monsters open the doors, the doors don't close behind them so that's another problem. I'll just do the first thing you said.