Did we ever see him?
Rachel claims to be the new Kip when Ross agrees to Emily's terms not to see her any more then Joey says... you're not the Kip. Rachel says Joey doesn't even know who Kip was... BUT there was a whole episode dedicated to Chandler and Joey arguing about Kip leaving.
He got married and ran off according to Chandler but Rachel says they froze him out.
A curious character indeed, this Kip chap.
Its not so strange if you consider that everyone sees things differently. Chandler probably had a different view of Kip and what he did than Monica, and Rachel and Joey only knew about him from Monica's or Chandler's accounts respectively. Also Joey and Rachel both used what they knew of Kip to back up their respective arguments, i.e. Rachel that he was treated similarly to her and Joey, that he used to be Chandler's roommate, and they both ignore/forget the rest since it doesn't matter to them at that point.
And I highly doubt Joey's ability to instantly remember a conversation of three years ago the second Kip's name comes up when we all know that at least half his mind is constantly occupied with food and sex. And how should Rachel know that Joey knows about Kip? She just knows that Joey never met him and probably assumes from that that he doesn't know about him either.
Yeah, lots of things are inconsistent in the show, but then that goes for real life too. People are forgetful, vague, inconsistent and often just can't be bothered to care one way or another. They wouldn't be human else.
No, we never saw him. Would you really have wanted to?
Ofcourse Joey never met Kip, but he knows of him, just like Rachel. Based on the stories, she believes she's the new Kip. But since Joey didn't know Kip, his opinion doesn't matter to her.