The moss and ferns will grow without any kind of fertilization, but they'll definitely benefit from it if you do choose to add some. They require ferts in the water column though since they don't root in the substrate where they'd be able to use the Rootmedic tabs.
I figure that much...but, I'm leery of adding ferts to the water column in a tank I'm trying to breed shrimp in. If there are no negative side effects...I'd certainly do it, although I have read that those that dose ferts have to do water changes quite more frequently which could stress shrimp, so I'm not sure that'd be for the best.
Maybe just a small dose would work for me, though I have no idea what exactly I should dose for moss/ferns/anubias. Suggestions?