JB, The forces that keep a wheel round are from the spokes, transmitted to the rim which itself spreads the load to the tire.
Since the spokes are steel, the added stress from hanging the bike will not cause "creep yield" in those parts at temperatures below 500F.
The spokes, rim and hub see added stresses but not out of the range of normal cyclic loading and so would not likely contribute to significant localized loss of spoke tension.
I have some reservation about certain wall-mounting hooks that generate even higher pulling forces toward the wall than are created by the bike's weight. Wall hooks should not contact the rim too close to the wall, lest the pull forces become almost infinite.
David Snyder
Auburn, CA USA
To a very good question that surely has wide interest: Is it safe (to wheel trueness) to hang bikes from their wheels, either single or double? Or, does doing so tend to elongate matters?
JB Froke
Pebble Beach, CA