yeah should be fine unless you get a psycho one or one that thinks it can eat things larger than it, but even an aggressive one would usually only be aggressive towards other cichlids that it views as a threat or something small enough for it to eat. with a knife and cat they will be different looking enough and act way different so he shouldn't bother them, will def be a cool tank thats for sure!
(P.S. since O grows faster than knife make sure to have lots of hidey spots for it and when they are small bgk can be shy about eating so make sure it gets enough food and it should grow fast enough and shouldnt have trouble with food once its larger)
