Dunno about the dog collars for sure, but as they aren't Mass Storage Devices and do firmware updates with WebUpdater rather than GarminExpress my guess is that they don't have a dedicated preboot mode at all. Older 'region-only' Garmin GPS devices without MSM are in a perpetual 'pseudo-preboot' and are seen by Updater.exe without doing anything, as long as they're powered and correctly connected by USB they are flashable. Have you tried connecting it to PC via the charging clip to see if it's recognised by Updater.exe?