Perhaps I'm not fully understanding a difference between logic level and the function of the TX and RX pins? I'm just wondering if an ESP can send, one-way, data to an Arduino. (I found that two-way communication would need a logic level converter.)
Arduino datasheets do not appear to specify logic level tolerances. It appears from this Arduino Forum post, it would work.
Is it universally assumed that 3v3 will be in tolerance for logic high? https://learn.sparkfun.com/tutorials/logic-levels/all