Many times someone else will drop off and pick up tanks besides the certified diver. Paint ballers also get air fills. Some people also use air tanks for airbrushing in nail salons and for running air tools or filling tires.
There is no DOT ruling that says some one needs a cert to get an air fill, there also is no DOT ruling that says a tank has to be VIP’d to be legal, and I’m not even sure there is any DOT ruling that says people can’t get O2, Nitrox or trimix either.
I think all that is dive shop stuff.