It is, if the Garmins are connected to public Garmin profiles or to third-party apps like Strava.
Otherwise, they function as GPS-signal receivers and only record data to the watch. (If connected to a phone or computer via the Garmin app/program, then Garmin watches will sync the watch data to the phone/computer.)
Ok, says they have Bluetooth and WiFi. I'm not sure I would trust the firmware not to be vulnerable to 0-day data exfiltration once the device is back in base.