Does anyone have any tips or advice of how to integrate a new junior QA Engineer into a established, highly technical dev team.
Have him be instructed by the enior QA engineer.
Make him read all the documentation you got.
Have the devs take some time to explain features to him. That way he should learn to understand their general intentions and practices. Start with the most esential/most frequently tested (types) of features.
Allow him to spend time with the devs: set up lunches, joint breaks, after work events, ... They should get to know and understand one another.
Include him in all dev-related communication (chat rooms, mailing/notification lists, accounts in all kinds of tools).
Make sure to give him independent QA assignments (i.e., the kind that he himself is solely responsible for) as early on as possible. He should become self-sutained ASAP.
Have him write test cases and update documentation of features he tests.
Just off the top of my head.