In general yes.
Athena at Home requires Internet access in all circumstances.
Athena for Clubs requires Internet access for certain use cases. It is however is designed to tolerate temporary loss of Internet access for day to day use. Specifically, Internet access is required for the following.
•Initial set up of your Athena range.
•Updates to the the Athena EST Units software or Network Manager.
•Support provided by Shooter's Technology.
•Certain enhanced viewing options with the Spectator Display (MM100).
•Periodic root certificate rotation.