Is a ground station radio license required for UAS operations in the US? When conducting UAS operations would a PIC or Spotter be considered a ground station or an air station?  The communications would concern a sUAS in the air, but the radio is physically on the ground.

I'm asking in the context of licensing within the United States.  As far as I can tell from reading the FCC's website, Air stations do not require a station license to operate, while Ground stations do.
Air -> Air, or Ground -> Air describes the ultimate path of the message. It doesn't describe what's being discussed. So:


  The communications would concern a sUAS in the air, but the radio is physically on the ground.


If the radio endpoints are both on the ground, then that's ground -> ground transmission. Put it another way - if a controller talks to a fireman over the radio, about an aircraft in the air, it doesn't magically become a Ground -> Air transmissions.

The definition matters primarily for technical and practical reasons (E.g.., Air -> Air radio will have a better range than Ground -> Ground because of nothing being in the way). If you're on the ground, you're a ground station - it's as simple as that.