I'm in the process of switching my wife's phone over from AT&T to Xfinity so we have both major networks covered in our travels.
I don't see any "HotSpot Only" plans from Xfinity however. You can hotspot from the phone like the other major carriers but they don't sell hotspot hardware or plans that I can see.
It may take a phone call to Xfinity or stopping at one of their stores to know for sure.
I may try putting the Xifinity SIM from my wife's phone into my Winegard ConnecT 2 just to see if it will recognize it and whether it will pull data after I activiate it. But that won't be for a few months since we are at out home in FL and the coach is stored up in PA.
Sometimes you can make it work but other times you can't. Here is one example....