Depends on your definition of legendary. Manaphay can breed to make a Phione, and Manaphy is legendary. You might consider Zoruark legendary. Zorua and Zoruaark can breed.
A legendary cannot breed under any conditions because they are classified in the undiscovered egg group (With the exception of Manaphy).
Baby Pokémon are designated for this group due to them being too immature to breed, while legendary Pokémon are included to prevent players from breeding them (with the exception of Manaphy). -Bulbapedia
Read more about it: http://bulbapedia.bulbagarden.net/wiki/Undiscovered_(Egg_group)
no it wont let you hatch the pokemon
no a legendary will not make a egg
