I keep Rams with my Discus...though I was growing out some babies in the tank and found that as they got bigger and more active, the Discus hid more....I traded the Rams for store credit at an lfs, kept one pair and now the Discus are out all of the time....so, I think the most important thing to consider when choosing a tank mate, is how active they are....I had to remove a school of rummy nose tetras a while back for the same reason....
However, having said that...the other night I went to the lfs to use up my store credit....and fell in love with a gymnogeophagus rhabdotus....it is absolutely beautiful....so colorful...with such a cartoonish little face...I asked the owner and he said that it would be risky putting him in the tank for the reason I stated above- he's kind of a hyper little fish....cleaning the plants, eating (cleaning) the rocks, eating stuff from the side of the tank, etc....but, being the stubborn person that I am, I bought him anyway......
I brought him home and at first, I think my Discus were completely irritated with him (and me
)...when the Discus swam to the back, he swam to the back...if they went up he went up....they couldn't escape him...he is like a little excited puppy....but now the three of them are always swimming together.....it's really pretty funny!
So, moral to the story.......yes, there was a point to all of that...
....there are exceptions to every rule....some fish will work that aren't supposed to and some some won't that should....