Running only one dual wheel loads the wheel bearings differently, most of the load is on one bearing and not shared evenly by both.
With both wheels on the hub the center of the pair of tires is close to the center between the two wheel bearings. With only one tire the center of that tire is outside the pair of wheel bearings.
I expect it'll work, but I would not overload it, or get close to the rated load.
If you run single wheels (from a single wheel truck) in the rear you would be OK as Steve points out, and no bearing issues, just tire and wheel load rating to consider.
Grigg
