ABSOLUTEY
, they add to the bioload... plecos especially
Actually, they don't recycle or absorb nutrients, this is an all too common myth. They are just like other fish, they eat fish food and they poop fish poop. The young of many species of plecos eat algae, but as they grow older they need to be supplimented with protein. Otos eat algae and need to be subsituted with veggies and algae disks once the algae is gone.
Otos and plecos do not eat other fish poop, to do so constantley would be hazzardous to their health.
While the addition to the bioload on otos is fairly small as they stay small and are not heavy waste produces, BUT it is just as much as any two inch tetra.
Most plecos, on the other hand, are heavy waste producers and need very large tanks with heavy filtration. Many also grow larger than 12'' and do so very quickly, adding even more need to good filtration and large housing.
As for the inch/gallon rule... it's not a "rule" at all, but rather something that has been dragged out far to long. Here is a post regaurding the issue posted by Richer in the FW newbie forum,
http://aquariacentral.com/forums/showthread.php?threadid=26409