From personal experience I have had all positive outcomes with my cray/lobsters and all of my 'aggressive' fish- even my now 6 inch über psycho lutino oscar, Gino. I keep him and my 5 inch lava red lobster in my 'evil' tank.
I have a sunburst lobster in my riverscape at my moms river monster sanctuary with my 14 inch red oscar, Bob, my 16 inch zebra oscar, Oscar the grouch, and my very large (unmeasured because of difficulty) giant upside down black cat (not African)- but he is also 10 inches and aggressive.
Lastly I have an orange cray, circus peanut, who is happily residing with a male and female betta, 7 celestial pearl danio, 5 longfinned blue/purple leopard danio and 3 longfin skirted serapae tetra. He's a little guy, only about 3 inches, I've noticed longfinned species tend to stay away from him. He did get picked on pretty bad before he was given to me, though, by a pair of Bolivian rams and 3 grown galaxy loaches....
Driftwood, preferably cavernous or a few pieces that are set up to make him an entrance on the top, java moss around the entry ways and fine grade sand underneath where your cons can't get in and a system of lava rock and decorative rock or driftwood structures covered with moss and a conservative amount vegetation will keep him happy and safe...
Inverts rule!! Good luck!!