Well I just tried it out and I was able to spectate as well as join a random battle (though I lost horribly... Really need to read those instructions o__o ) I have my Wii set to obtain IP address automatically, don't have any ports forwarded (apparently this doesn't help things much anyway according to
this), and it seems to work. Mind you, my Wii isn't connecting directly to the TC, but rather to the b/g network created by my Linksys WRT54GS. And with my setup, it's effectively behind 2 firewalls and it's still working. I'll try setting my TC to a b/g/n network and connecting the Wii directly to that.
btw, have any luck or still no go? And when you go to your network settings in your Wii and do the connection test, does it give an error?
Edit: I just tried setting my TC to b/g/n network and connected my Wii directly, both with static IP and with dynamic IP, and I was able to connect and play online. Again, no ports forwarded to my Wii, but the dynamic IP was lagging horribly towards the middle of the round (though doubt that's from my end).