I'd be a little hesitant about using that rubber coating in a tank, no telling what it could leach into the water column even after it has cured, if it ever really fully cures. It would come down to the stability of the material at the molecular level, I'm no chemist but some of those tool dip products contain some pretty nasty stuff.

As far as hitching posts for seahorses go, live macroalgaesare great, however to thrive they tend to need a bit more light than you'd want in a higher nutrient system, else the nuisance algaes will get a solid footing as well. Angel is using a combination of artificial plants and corals for her H. Reidi with great success. For some reason hair algae like to grow on the plastic, which she rotates into another tank where the tangs and lawnmower blenny pick it completely clean.