This is nothing special when it comes to pokemon. It is possible for a one and a half pound cat to have sex with a 20 ton whale in a pokemon world. I've done it before. I laughed.
With a 20 ton whale. I'm not joking. Damn it, I was going to post that in response, until you did. >.<
Not legendary pokemon or pokemon of the same gender. And there are also Pokemon that aren't attracted to each other.
****!!!!!! Well duh. But people still try to figure out if things in fiction are possible in the real world.