Most of the bark damage occurs from a "moving rope" system over the wood. Using a "fixed rope" system where the rope does not move, like with SRT, incurs little to no damage. A simple tie off of a hammock overnight or for a few nights would incur little damage as well because the rope/sling is not moving-abrading the bark surface.
A trees' vascular system is encased in a rigid substance unlike the soft tissues us animals have to endure. Therefore they are more tolerant to things treading or hanging from them.
Waving from a treetop,
Peter Treeman Jenkins