I am going to cite precedence here and predict that Santino is not going to be competing in the Elimination Chamber tonight. I believe he will be ambushed tonight, similar to how Kofi Kingston was ambushed by Edge at No Way Out in 2009. This happened as Kofi was on his way to the ring. My rationale? Santino just doesn't have any business being in this type of match—he is simply a joke character intended for comic relief.
The question is, who will do the ambushing? I am predicting that it will be Randy Orton, but there is an outside chance it will be Mark Henry.
On Smackdown, they tried to sell that Orton is "kayfabe" injured, and Teddy pulled Orton from the Elimination Chamber match. Supposedly, Orton was "concussed" by a shot to the head with the title by Daniel Bryan. Obviously, this is not enough to keep the Viper out of the match. How many times has a wrestler been hit in the head with a belt, only to return on the next show?
Finally, having Santino in the match instead of Orton is just not good for business. People want to see Randy Orton, they pay to see him. While Santino is funny and entertaining, he is a huge downgrade from Randy Orton. Moreover, Santino has no shot in hell of winning the match. It was a nice underdog story; Santino recently won a battle royal on Smackdown to earn his spot in the Chamber.
However, I see history repeating itself tonight and Santino being ambushed by either Orton or Henry as Santino is on his way down to the ring.