Is it guaranteed if I breed a delta with a d. ditto, I get a pre evolution?
Yes, you get the first evolution stage in most cases but 2.
1)Delta Munchlax - Breed a D. Dittio with a D. Snorlax holding a Rose Incense
2)Delta Budew - Breed a D. Ditto with a D. Roselia or D. Roserade holding a Nocturne Incense.
Delta Munchlax, Budew, Pichu, Elekid, Magby and Roilu are baby pokemon, they can only breed with D. Ditto after they evolve.