The height is just part of the issue. The camper pictured above sits on the bed of the pickup and that weight is directly transferred to the frame and wheels.
In the OP's example the load is not directly sitting on the bed. Will it be safe? Ask that question if that driver needs to do a emergency maneuver or slam on the brakes.
The driver needs to take everything into account when hauling heavy loads like that, not just the weight.