Which south americans are you talking about? Oscars acaras and severums will be fine. Some of the more agressive ones may harm the pleco. Make sure pleco is larger than the cichlids. Rhino are pretty much omnivores.
They should do fine as long as they aren't with a dovi or some thing similar. In my experience shrimp pellets help keep them in better health than algae wafers but they should be given a mix of both from time to time.