Totally no problem. I have a G6, albeit with GOogle Now launcher not TouchWiz. Just installed Gear app and Samsung Health app and it was a done deal.
The main requirement is you have to have Bluetooth 4 - the watch can't talk to anything that has only earler editions of bluetooth. (BT4 has the "low power" mode that things like watches need if the battery life is to be more than an hour or two!) You can't add BT4 to an older phone just by firmware upgrade.
I presume my Tab S doesn't have BT4 and this would be why it says it *isn't* compatible with the apps.