I spent the last hour scourging the forums for iPad apps that work with PS3 Media server. I finally found something.
I am using PMS 1.70.1
I set the default renderer when automatic detection fails to iPad / iPhone.
I forwarded port 5001 on my host machine.
8player Lite (the free version) seems to work.
Delete/lock this thread or whatever, just let it be known that for now, 8player Lite can play .mp4 and .avi files.
EDIT: Something worth mentioning, 8player Lite will not allow you to play any files other than the first five in a given folder, so you will want your movies to be in their own directories and you may need to tediously create unnecessary directories for your episodes.