Yes. If you have Beast Bucks credit on your account, it will be deducted first when you pay for the rental. If your Beast Bucks credit does not cover the full rental amount, the missing amount will be deducted from your main payment method.
P.S. It may take a few moments for Beast Bucks credit updates to appear. If the amount of the credit has not changed immediately after the end of the rental, please check again in a few minutes.