I just thought about it. It said it is female in bulbapedia here: http://bulbapedia.bulbagarden.net/wiki/Pleasant_Forest_(Dream_World_area)
all eggs hatch into whatever pokeball the mother is in. except I believe with ditto as the mother it will always be a standard pokeball. Nidoran♀ was in the dream world, I remember it took me forever to finally catch one so I could breed my sheer force nidoking.