I am not much of an explainer - but I can try and answer in my own way and as best I can:
OK - so you are wondering about "your data", and also wondering about the extra bandwidth used to track all these other peoples devices right?
"Your data" is not really doing anything much. Your phone will be relaying a small amount of data though. You are connected to the cell phone network and bleeping a few bits and bytes here and there just as the phone would normally be doing. You won't be sharing your location BUT at the very same time you are actually sending some information over the cellular network that IS your GPS location data AND ALSO the Identity number of the Bluetooth Tracker tag. That sounds a lot like the same thing as sending "your iPhone GPS coordinates" - except this data is encrypted and dissociated from your iPhone and is instead tied to the identity number of the Bluetooth Tracker tag. This sounds a bit twisted, but that's how these things do work.
Apple will probably give us more information about how much extra battery drain every iPhone user on the planet will have to accept - but actually they will be stating that this amount is equal to zero - and that is probably right. I suppose it is a trivial small amount of data, and Apple could claim that the data has always been there anyways and had to be sent, but now they are hitching a free ride with the Bluetooth tracker ID number hidden in there.
Voila. Verizon has no clue whether the tracker tag is an "ATT" customer or anything else. In fact if they designed it right, Verizon nor ATT nor anyone, including YOU will not know that you have tracked any bluetooth tag at all. Your phone exists on a cellphone network or wifi, and all this tracking stuff is done in the background anId hidden within existing nominal traffic. I made all this up, but never let facts get in the way of the truth. Someone who knows more may correct me, but how often am I wrong - almost never right?