Ladders are not in V1 so you wont be able to use them. If you have them in games made with EA then you will have to replace them currently with some other method of movement upwards. i.e. stairs - not much option really. This may cause you some difficulty in having to redsign your levels.
I dont see any reason that you could not effectively overide this in theory though you would get problems when actually trying to climb the ladders due to the introduction of physics into the engine.
Problems would be most apparent if you say have ladders stacked one upon the other so you have a "high ladder".
Ladders may be brought back after V1 so you may like to leave your levels as is and wait for such time....but who knows how long that may be?
Efferctively there is no substitute for a ladder in a game so....
A comment from TGC may be helpful on this issue.