Front tires are the most important when talking big rigs but trailer tire blow outs have caused roll overs.Just had one in the Spokane news.But as your probably aware of, one blow out on the trailer usually doesn't do that because of duals...
Any trucker that purposely puts sub standard tires anywhere on his rig for whatever reason is putting other motorist in harm's way.
As for RV trailer tires, it is my opinion for my use being mostly backcountry Rocky roads, a tire designed for the weight and abuse this gives to a tire is in order, same goes for hauling heavy loads of firewood.
You should see all the ST tires blown out on small trailers hauling firewood.Usually you will see at least one per week or so off the side off the road....
There's a lot of things to skimp on, tires ain't one of them.