i bought deluxe edition with my gog acc where i have my gwent acc,and i didint get any rewards like cardbacks etc

Same issue for me.

Also, inside Gwent, Rogue Mage does not show up as "owned" in the same way as Thronebreaker does (even tho it's clearly in my GOG account, and I've bought the deluxe edition).

Ok, so the solution is that you have to login to Rogue Mage before playing Gwent to get the rewards.
After that you can claim them as a contract.