No, youre right, I mistakenly read hitag as hidtag for some reason.
I went and did some research quick, and they aren’t necessarily encrypted, it is just a possible mode. I suppose we would need some more data, and possibly the full memory dump from the chip. It is a LF chip with less memory than a T5577 and the modulation/coding of the two chips could be lined up, as the T5577 has bi-phase and manchester modes, which are the two possible modes of modulation used by the HT2, so I could see cloning it being a possibility for sure, unless I am misunderstanding again. Maybe not as simple as a HID card, but I think it could be done with a bit of work and experimentation, perhaps with a T5577 card to test with so as not to brick the implant.
links to the spec sheets for both chips
HT2
T5577
Edit was for spelling