Ukraine has unutilised domestic production capacity. They can turn the good money the Gulf states will be paying for the drones into more drones for the frontlines.
When people say ”time is money”, there is usually an amount of money that makes you go ”… but then again a lot of money is also money” and give up some time in exchange for that money.
Wartime resources are similar, in the sense that they’re at least partially fungible. Maybe the amount of money the Gulf states are willing to pay for borrowing those people buys you a lot of the other stuff.