The terms and conditions say it should include the original strap and charger. How strict they are with this I don't know, best off trying to get customer service and hoping they actually have a clue about it. If you don't have it and they need it, it might be worth having a look on ebay for one.
Do you think they will accept a Huawei Watch GT (original)? I suppose it could be argued that it isn't really a smart watch as you can't run third party apps on it.
I don't see why not, it's not a "dumb" watch. If it has a processor instead of gears and a screen capable of showing more than just lines I'd say its a smartwatch. Their T&C are very vague on what constitutes a smart watch. I was half tempted to trade in one if those cheapo kids watches that take a SIM card