Yes, you can use it as your deposit, but...
The Royal gift cards I purchased in the past were a Royal pain in the ***.
You have to book directly with Royal then transfer it to your travel agent. After a certain amount of time and prior to a certain amount of time.
I'm sure some will say; "Not a big deal", but they weren't worth it for me.
Also, Keep the card because if you have to cancel it is your receipt. (though they may keep a record on your account)