Well, we've seen no pics of him so far and the big question is, IS TAILS IN SA2??? The answer is

No one knows!

The official Dreamcast magizine in the UK stated:

In a recent interview with Yuji Naka, the guy who created Sonic, Official Dreamcast Magazine were asking questions about Phantasy Star Online and the new Sonic Adventure 2 game coming out early in 2001. When asked if Tails was going to be in Sonic Adventure 2, Naka replied that no he wasn't. When they then asked if Tails the Fox would make a comeback he said he couldn't say anymore which suggests that Tails may come back seeing as most developers say things like, 'Sorry but we have finally scrapped this.' I hope this will end months of specualation of Tails being in SA2.

And Sagesages said this as well:

In the Preview Yuji Naka it is made clear that Only Sonic, Knuckles and Dr. Robotnik are the surviving members of the original cast and he points out that the Dark Hedgehog plays a big role in the story. What ever the Dark Hedgehog is it will be big as even Yuji Naka refuses to talk about it.

That should end speculation right there, two sources said Yuji Naka himself said no Tails, but WAIT! There's more. Gamespot got their hands on a preview and had this to say:

Sega first showed us a brand-new trailer for the game that showcased Sonic Adventure 2's enhanced graphics and hinted at the storyline. From what we could tell, Sonic, Tails, and Knuckles are the primary heroes in this game, and their quest involves both Dr. Robotnik and a brand-new character. Though the trailer wouldn't show the character in full view, it did show several close-ups of his face, enough to allow us to make an educated guess about his identity...

So, the answer to this question still remains unanswered after all this time. Hopefully the real answer will be revealed soon...