Yes, it is correct, and "formally correct." It is similar to using KO and other initialisms as verbs. However the apostrophe is used to signify that something has been left out. And in this case you usually leave out the e of the ed ending.
He KO'd me in the sixth round.
Other examples from Oxford
‘In his first fight as a pro, Foreman KO'd Don Waldheim in the third round an hour before Frazier and Quarry fought.’
‘Those days may have ended when Mike Tyson got KO'd by Buster Douglas.’
‘His final 5 bouts following the McClellan tragedy ended with a record of 2-3 with Benn being KO'd on 2 of those occasions.’
‘Conn had KO'd his last four opponents, including heavyweights Buddy Knox and Gunnar Barlund, both in the 8th rounds.’
Examples of using TA:
I TA'd Chemistry 101 for him last semester.
Did you like TAing for him?
I'll TA for her next semester.