Also, I just acquired Spirit Wolf Totem and can say it's amazing as a Justicar Tank. It's up time on me was well over 50% and I saw it on 4/5 party member simultaneously. I don't know if it's better or worse than Sacred Heirloom of Eth since I have only ever seen that one heal basically Melee but both are still very nice for Cleric Tanks.
Sacred Heirloom of the Eth until the nerf is the best trinket, especially on justicars. After that, I'm not sure how it fairs.
I'll also state that main tanking in Raids as a justicars is quite viable. My guild is 5/9 (4/5 GSB, 1/4 RoS) and our primary tank is a justicar. However from what little I know about Greenscale himself, they are far from the optimal tanks for that encounter.