Can you teleport to Rek'sai tunnels?

Yes, you can use teleport on tunnels. I don't have any proofs but I successfully teleported myself to a tunnel during a game. I don't remember if the tunnel was on cooldown or not but I don't think it matters.

There is a message here that confirms it: (In french)

http://forums.euw.leagueoflegends.com/board/showthread.php?t=2013782