No. They are using an app on the phone. The dock connector allows the app to communicate with the head unit.
Tethering, by definition, would mean that the head unit used the phones Internet connection to obtain its own IP address and communicate independently with whatever it wanted to. It can not do that.
If you understood the first thing about networking, you would understand why it's not the same thing.
Well in fact I did talk to Toyota support about the fact that BT was not working, and they told me that it was a known Apple bug. Could it be that I spoke to a support engineer that was not knowledgeable, or that was trying to shift some blame onto Apple! How could that be!
Here's a 'stop-press' on this. My phone does not even connect to Entune even when I plug it in, so I'm guessing I'd better talk to support again!