I've only had a brief experience with the Gramma and my shrimp, a coral banded. I bought a purple pseudochromis only to find out that him and my shrimp were super incompatible; fighting, stand offs and nipping, (impulse buy argh)... anyhoo, I brought the fish back to my LFS and told him that I wanted to exhange the pseudochromis for a Royal Gramma. He told me that I would get the same results with the Gramma that I would have with the pseudochromis. I had read otherwise online of course. So I brought the Gramma home but he did not survive more than two days. I'm suspecting that the Gramma was sick from the LFS since we have had previous similar experiences, but I could not say for sure that it wasn't due to stress or fighting.
Note: I only trust about 32 % of the things that come out of my LFS's mouth.
Prolly not helpful but my two cents.