If you have restricted flow in the return line from the flow divider bypass/motor return to the tank, I think you could be setting yourself up for heating problems and may want to install some sort of cooler.  Our old JD 1380 mowco didn't come out with a cooler but they came out and installed one after the sale.  It runs constantly many hours per day - and hasn't caused any problems over the years except hoses; but it was designed to do that.  Judging by Milo's experience, if your pump is designed to take the required pressure, you may be okay.  If the pump was not designed to take the required pressure, you may have problems.  I'd suggest getting the model numbers off of the pump and inquiring about the capacities at a hydraulic shop.

I loaded taters last week where they used a straight truck for a meter box between the sorter/piler and the piler for loading the semi's.  That belt ran all morning long but not with a heavy load, only stopping while one truck pulled out and another backed under.  I wondered if it was designed to run that way, I'm not aware that they had any problems with it heating.  I believe it was electric over hydraulic with a variable displacement pump.  Trinity make the gasoline driven variable displacement hyd pumps which would probably be great in your application; you would only need to pump the amount of oil that is needed to get the desired belt travel.  The problem with having those units is that the neighbor's without wet kits will constantly want to borrow the trailer.  :-)