OK, lets make a few assumptions.
1. The spokes are steel alloy and inherit the mechanical properties of steel, per se
2. The rim acts like a hoop in compression and it is the spokes, not the rim, that are responsible for withstanding any radial stresses.
3. The ambient temperature while the bike is hanging is well below the level where steel undergoes any appreciable "creep" under stress.
If the above 3 assumptions are correct, then the stress of hanging the bike by its rims will not result in any permanent deformation of the wheels.