…..eligible, except… If you line up that way with a guy that has a number in the 50-79 range, you have to tell the linesman. Evidently, Ziemba forgot.

The tackle may legally catch a backward pass, but not a forward pass. The rule to exclude forward passes to tackles was made in response to Bear Bryant using it in the 60’s.
http://sports.espn.go.com/ncf/columns/story?columnist=maisel_ivan&id=4537995

There’s not much on the net about this specific play. The best I could get was this discussion by refs.
http://www.tidefans.com/forums/football/77142-officiating-question-not-bashing-any-specific-call.html

College Football
NCAA rules are less permissive than NFL rules and require that the five interior linemen, numbered 50-79, never line up as eligible receivers. See rule 1, section 4. Thus, an offensive tackle can never become a tackle eligible. However, a defensive lineman can play as a tight end if his number is not between 50 and 79 (defensive players have no positional numbering restrictions in the NCAA).

A similar play is allowed from a kicking formation, where the requirement that all five linemen wear 50-79 is waived. During a fake field goal or punt, a team may line up with extra tight ends and receivers making it not immediately obvious to the defense which players are eligible and which are not. (However, this exemption can only be taken when it is obvious that a kick may be attempted, for instance on fourth down, in the closing seconds of a half, or similar situations. It cannot be used on every down at the college level.)
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NFL Football

For example, by official National Football League rules, players with the numbers 50-79 and 90-99 are ineligible receivers. The quarterback or offensive captain informs the referee that a usually ineligible receiver will be eligible for that play. The referee then announces that the ineligible number “x” is reporting as an eligible receiver. This announcement is made using the referee’s microphone so both spectators and opposing team can hear. The eligibility is good for only one play and must be done before every play in which the offense plans on making the player eligible.

http://en.wikipedia.org/wiki/Tackle-eligible_play