re: Why was Dabo so pissed at the refs after the onside kick?

I believe the fair catch is actually irrelevant to the call. The kicking team is not allowed to interfere with receiving team making a catch on the kick.

On Clemson's kick, not only did the South Carolina player call for a fair catch, the Clemson player went through him to catch the onside kick.

A well coached special teams is always going to call for a fair catch. It kills the play upon the player making the catch. If he doesn't call for fair catch, he's probably going to be leveled and risk a fumble.

Edit: And as prior poster mentioned, bobbling is protected.