Make it so.
Quote from Skullboy:
I think what would be a separate category would be zips and no zips. That way, certain glitches could still be used but the player wouldn't be entering any walls,floors, or ceilings that they would be if they were zipping. Just an idea.
That sounds pretty fair, although like I said, there are two main types of Zip in this game (horizontal underflow and normal) which are pretty different in that HU skips an entire level.
Also "zip" would have to be defined as technically I don't think the first half of the Ice Cap glitch is a zip, would need confirmation from someone who actually knows how that works though.