[B. W.]

No, many steel wheel / radial combos on the road. He may have been talking about cleaning the rust from the bead area to prevent bead leaks. Or he may have been taking about tube type wheels.

Tube type wheels do not have the safety lip to keep tubeless tires on the bead when they go flat. I have run tubeless tires on tube type rims for many miles, no issues. But it could pop off of the bead when flat if the conditions are right (or wrong, however you want to look at it)