Loaches typically do fine as do catfish and plecos. I think it's kind of a natural symbiosis. Because the loaches and catfish are bottom feeders and the pleco takes care of the algae on tank surfaces, I guess the cichlids don't really see them as competition for food. But, like poppab02 alluded too, anything too small becomes cichlid food.
I had a Gold Severum years back along with Neon Tetras (back in the days when I bought fish just because of how they looked
.) Anyway, I never did see the severum bother the tetras. In fact, they seemed to coexist together quite well. until I noticed that my tetras kept mysteriously disappearing. After this happened a few times, and I never found any remains, it finally dawned on me that this rather large severum was snacking on my tetras.