Alright so I have 1 iPad with the VTO added as a local device, not logged into an account.
Another iPad, VTO addes as a local device, logged into an account.
The first time I went to test, only the iPad that is logged into an account rang, but only after the VTO had rang the max amount of time and had hung up.
The second time I tested, both rang, but also only after the maximum amount of rings.
It used to function that as soon as the doorbell was pressed, all devices (both VTH's and the iPads) would all ring at the same time. Not wait for the 5 or whatever rings of the VTO and then push the call to DMSS.
I don't know what's going on lol, but if it's as you said having an account logged into the APP is mostly only for saving of the messages/notifications (which I don't care for atm) then it don't see why it would matter ?