The main difference between an Exhibitor & a Sponsor in the Accelevents system is going to be the level of interactivity. While Exhibitors have a higher level of interaction with attendees, Sponsors by default have a higher amount of image placement.
It is possible to have the same organization/person/company listed as both a sponsor & exhibitor.
Key differences
Exhibitors
Interactive booth in Expo area
Logo placement on Event Landing Page
Live reps to chat with attendees
Sponsors
Logo placement on event hub Lobby
Logo placement on Event Landing Page
Placement in event's lobby carousel