Yes, it is correct grammar. This usage is especially common in informal English. It is similar to using KO (to knock out), RSVP ("to respond"), cc ("to carbon copy) 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](https://en.oxforddictionaries.com/definition/us/ko)

>‘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.’  

For RSVP:

>Did you RSVP the Smiths yet? 
>
>Yes. I RSVP'd them last night. 

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. 

[but note that these examples for TA'd are anecdotal, **not**, as it might appear, from ODO/LEXICO.]