I only have one ZBT-2 but my understanding is you can have two, one for Zigbee and another for Thread. On the products FAQ under the “Why do I have to choose between Zigbee and Thread? Why not both?” question it states “strongly recommend dedicating a device to each protocol”, which would mean you’d need a second one. Honestly if I ever have a need for Thread my plan is to get a second ZBT-2, so I hope I’m right. I’ve also seen people mention they ordered two. I’d maybe wait for someone that has two to reply just to make sure though.
It is possible, however I will admit that I’m not positive about how HA’s auto-detect and setup handles two ZBT-2s, but it should be able to distinguish them by serial number. Worse case is that you may have do some manual config.