i think i found some clues that the robin in teen titans is tim drake. first of i think teen titans take place after the flash back scene in batman beyond; return of the joker.
1. in GO ! robin calls being with batman kid stuff, the same thing he says in batman beyond return of the joker when terry questions him.
2. i think his personality is different from his in the the batman adventures because this is after the joker had tortured in the flash back scene of return of the joker. making him more stern and serious.
3. i think the future scene with nightwing is only a possible future and not definitive.