It's a good idea to flush out ANY engine that you get, new or used. While checking it, also look for flashing that might later break off...remove with a #11 blade. No manufacturing process is perfect and although you might get it repaired or replaced free, it's easier and quicker to check.
It's SORT of a good idea on some engines. I would have not expected a problem in this case.
I have seen a fair number, that is, more than a handful, of engines that appeared to be unnecessarily disassembled and then never ran properly. If we are talking a new PA or RO-Jett, I would discourage anyone from doing more than the very minimum work to get the venturi as you like it, but certainly not a "disassemble/clean/lube" like it was a McCoy 35 or even removing the backplate to flush them out. The chances of messing it up is higher than the chance of something actually being left in the engine.
I don't just mean people who have never done it. It's not rocket science (heh!) to get an engine apart and back together properly, but some of the cases I have seen were from people who should have should have known what they were doing and in one case is considered an expert of the highest order.
I also have found no need to do this on most current consumer engines. I run the OS's straight out of the box and so far no damage. The likelihood of a problem is higher but still, it's a small enough probability that I would rather risk that than messing something up.
The only engines I would recommend cleaning out are NOS or new Foxes, used engines (since you can't tell if they have been crashed and left dirty), or a "cottage industry" supplier other than Randy or Dub. Most of the latter mean well but unless you are sure, I would take off the backplate and flush them out. I have seen too many of the reworks eat themselves up from left-over machining debris that it outweighs my reluctance to avoid a possible assembly error.
Brett