If both of the 4G cellular modems have decent coverage (and appropriate data plans) then yes, that could work with the right software. I don't know if oovoo is the right software for this -- haven't heard of it before -- but in theory, yes, video is just data with a certain bandwidth requirement.
If you only need a mile or two, you could consider 5 gHz "FPV" cameras/transmitters/receivers as used in the quadcopter/drone hobbies. For the stronger transmitters, you may need to get HAM radio operator qualified, but that's not terribly hard I've heard.