I'm wondering why the Road Map on the main Surf's Up page hasn't been updated with Method's updated Road Map.
Personally, I say that it is worth it to unlock Z before starting since his basic board is almost Nirvana Level. Remember, everyone has a different starting board with different stats.
Also, I've tested the board unlocking with the different codes, and only Unlock All Boards does affect unlocking boards normally. I'd say that this isn't really glitched per se since it seems to always happen when using the code.
One last thing. If you do end up using the Unlock All Boards code, and then notice that boards aren't unlocking later on, all you have to do is exit out to the Save Game Selection after the Title Screen. Or just go all the way back to the Title Screen and load your saved game. Any cheats entered will no longer be in effect.