There are several species of "jewel fish". The genus name is Hemichromis and there are about 11 species. Chances are they can all cross but I wouldn't really suggest it, not if you intend on selling them anyway.
Jewels are some of the toughest little bastards around they are not going to get punked by a JD About breeding them with something else huumm good luck and you can try but it won't be with a new world cichlid that's for sure better off trying something old world. Still they are great as is just enjoy the fish
My jewel got beat up by my JDs. I am not giving blind advice. I had this happen. It all depends on the size of both fish. And I had three JDs in with one jewel.
not saying it could not happen but if you like to trade story's I have had one beat on a JD twice it's size. Depends on the fish and their size greatly and size of tank