No.
Its totally possible to breed unowns. you only get a bad egg if you use too many cheats at once on ar/GameShark or try and breed a legendary with another Pokemon e.g: another legendary or ditto. Just bacause a pokemons got no gender doesn't mean you cant breed it, i mean, look at ditto.
You cant
I believe you obtain an unown, or they're incompatible.
Every Pokémon that can be bred. Includes all Pokémon except legendaries (excl. Manaphy and Phione), Ditto, Nidoqueen, Nidorina, baby Pokémon and Unown. Ditto can breed with Pokémon that are genderless.
Ditto can mate with all 'breedable' Pokemon. So the things that it can't breed with are; Legendaries - except for Manaphy, 'Baby' Pokemon - Pichu, Igglybuff, Tyrogue, etc, Unown, Nidoqueen, Nidorina, and another Ditto.
any Pokemon can breed with ditto except legendary Pokemon and ditto. in other words, you can't breed a ditto with a ditto
Legendary Pokémon (excluding Phione and Manaphy), baby Pokémon, Unown, Nidorina and Nidoqueen cannot breed whatsoever. Pokémon with gender unknown (besides the aforementioned Pokémon) can only breed with Ditto.
anything can breed with ditto.
Nothing. Since a Ditto can no breed with another Ditto. They will produce no egg.
Any Pokemon can breed with ditto.
yes ditto can breed with empoleon
Any Pokemon that can breed, can breed with Ditto.
Any Pokemon that can breed can breed with a ditto.