No, the idea is connecting devices to the Sonoff so it can control them directly.
Now, for Matter devices is a Matter controller, so you could use Matter multi-admin to control your devices both from SmartThings and the panel, but that would not be “integrated into SmartThings”, just two parallel control methods.
Edit: Or maybe it’s possible, but it’s going to be cloud based so not really worth it: SONOFF NSPanel integration - #15 by Edgar_Cantu The API should be the same.