Guys - let's get real here. ETLs/TLs will talk to employers. I was a TL, and I did it multiple times for TMs over the years. It was always for TMs who I liked, did a great job for me, and I did it as a personal favor for them. Did I ever tell anyone else I did it or admit to it? Hell no. But guess what? It's illegal for that other employer to record you on the phone with them, so there is zero evidence you ever did it. In other words, it is 100% risk free unless you are a complete idiot and go around telling people you did it.
Before I got my current job with Sony I had the one ETL in the store I trusted give me a reference to my current manager as a favor to me. How do I know he did it for me? Because my current boss knows things about me I never told him that my ETL knows.
We had one ETL a few years ago get hired by the FBI. Two agents came in our store doing a background check on him before they hired. Think our STL talked when they came in flashing badges? Damn right she did. Two hours straight in the STL office with her. It was the talk of the store for a while.
So if you are Mr "No body likes me TM", then yea, no ETL/TL is going to say a word about you. But if you are someone particularly liked and ask the right ETL/TL you will can get them to talk good about you. If you are absolutely hated? Don't put it past an ETL to talk trash about you in private on the phone and then never admit to having done anything.
It happens. All the time.