Do it and let us know if it all works out. Where does it say Amazon GC?
I did it on a business trip a few days ago. It was direct with Upside. It was only $100 though. The rewards showed up right after travel. There are a lot of options for redeeming including Amazon, Airbnb, Best Buy, eBay, Home Depot, Target, Gap, Lowe's, Nordstrom, etc.
The way I understood it is I would earn a $100 GC after every $600 in travel booked with them.