Here is my experience so far in Australia.

Melbourne Marriott, gift cards accepted without issue, saved myself 2% credit card fee.

Sheraton Grand Mirage Gold Coast, no idea how to process gift cards even though I notified them day before checkout. At check out, they asked me to leave gift card with them, and they would charge the balance on my credit card on file. It took about 2 weeks for my gift card to be zeroed out and the balance owing (about $8) was never charged to my credit card.

Sheraton Sydney, no idea how to process gift cards even though I notified them 2 days before checkout. Charged full amount to my credit card plus 1.5% credit card fee. No goodwill gesture. I have since been advised that they are ready to accept my gift cards for next visit.

Westin Perth, no idea how to process gift cards, but mgr agreed to waive 1.5% credit card fee. FDA tried to tell me that credit card fees were built into the price in NA and Europe. However she couldn’t explain why I paid $300 for a $300 gift card. Apparently they will be learning how to process gift cards in the next few weeks.