I think this would be more of a trial and error setup. It may work great, or it may end in disaster. They both live in the same niche in the aquarium, the bottom. With enough teritories, and some good line of sight breakers I think that it has the possibility to work out.
Are you buying each as a 'pair' as in, they are adults and are breeding, or are you going to get some juveniles and hope that they pair off? I think that by getting juvies you are more likley to sucseed in this, however it would also add a lot of stress on both rams and apisto's once they started becomeing of breeding age and pairs started forming, as teritories and hidding spaces are going to be difficult to find. Having an extra tank to put the 'cast offs' in might well help save the lives of the fish that haven't paired up and allow you to either keep them in another tank, or sale them back to the store or someone else.
Do keep in mind that my thoughts are just guess work based on what I know of each. I've never tried this setup myself.
I know that the apiso cacutuoides and agassizii are often seen in a more community setting, but a larger or more robust species may be needed to live and breed in the same tank with rams. Then agian, the opposite may be best in getting a more docile species.
I belive that the males have more elaborate fins than the females, but not sure that this applys to all the species.