Assuming you mean he became a TE on the LoS then he's dirty. He was either off the line then moved onto the line, so he had to have moved forward, or he was already on the LoS so he cannot "motion" to another position on the LoS.
If you mean a TE position that is still off the line, then it depends. If he's facing the LoS while in motion and shuffling sideways but pauses as the ball is snapped then that sounds ok. If he jogs over then turns to face the LoS or puts a hand on the ground then he needs to be set for at for "1 second."