When the daycare man says the two don't seem like each other in ORAS it means there is a 20% of producing an egg after 256 steps. If the egg does not appear, then you must move another 256 steps for another chance at an egg. If it's seriously taking forever, which has happened to me before :/ then you can improve your chances by using a traded Pokemon as a parent, using two Pokemon of same species (if possible for your breeding purpose), or simply trying a reproduction of the same Pokemon you're already using from the same place you found it (because if IVs change, the egg calculation also changes).
Good luck!