Hi John,
You can use other midi files within AD2.......I do use EZ drummer's midi files in AD2, but the name/tags of the files don't cross over (meaning you'll have to practically name each file after importing them). Not sure if this naming issue is an AD2 prob. or something from EZ that stops the text from crossing over. I haven't imported/used any other 3rd party midi to verify this.
I can't remember the actual path of the folder where to insert these midi files (not at my DAW right now), but if someone doesn't chime in first, I can post it once I get home.