Samsung staff don’t officially read this forum. (There’s another forum over at Samsung that they do read. This one was started several years ago so that smartthings customers could help each other.)
That said, lots of people in this community do use the Gen 2 iris keypads with SmartThings. It still won’t give you the kind of security system that you had with Iris for a number of reasons, but you can certainly use those devices if you want to.
Read the following FAQ for discussion of the differences between the ADT model hub and the other smartthings hubs when it comes to security:
FAQ: Confused by "Regular" Hub and "ADT" SmartThings Hub. Need clarification (2019)
Anyway, there are several different device type handlers (DTHs) which work with the iris Gen 2 keypad.
Most are offered free by other community members, but for locks and keypads I think it’s worth it to pay the $40 lifetime license fee for access to @RBoy apps. It’s just one license fee and then you get access to the whole library.
You’ll find this is a very popular add on in the community, and they do offer their own support. It does mean using the classic version of the SmartThings mobile app and installing custom code, but you get a lot more features by doing that.
On the other hand… We have been told that eventually the classic App go away. But not when. So there is a risk that you will lose that investment in the future as well.
The alternative is to wait until smartthings brings out the keypad that they announced in January 2019. Obviously they know they need one.