You bet. Anything along those lines that hasn't been treated with/for anything (preservatives, so on). I feed shrimp, clams, oysters, squid, scallops...and so many others. It's mainly for my polys, but the cichlids love it, too.
lots of pellets and flakes actually contain salmon (sometimes skins). I do agree with killerfish that the fat could be a concern. I personally feed my fish shrimp sometimes.
As killerfish said, white meat fish is better to feed. Salmon will make your water pretty messy. Some cichlids will enjoy raw fish, while others will not be interesed. My GT eats anything I put in the tank, including tilapia and shrimp, while my Argentea won't touch either.
At least in my experience with Firemouths they're very susceptible to bloat from it, I lost 3 sub-adults using a custom 50% seafood 50% vegetable and spiraluna mix a few weeks after starting to feed it; after a few days the meeki were lethargic and refused to eat. The same batch was used with great results in multiple other tanks stocked with healthy Central and South Americans such as Salvini, Severum, Acara, etc. without issue.
I was also contacted on another forum regarding someones incredibly similar experiences with seafood and Firemouth.