If the listing broker is offering compensation on the property, should my buyer still include a request for compensation from the seller in the purchase agreement?

No. In a scenario where the listing brokerage is offering compensation, the brokerages should execute a Compensation Agreement Between Brokers. If the compensation is coming from the listing broker, it should not be part of the purchase agreement because the listing broker is not a party to the purchase agreement. In a scenario where a listing brokerage is not offering compensation to a buyer’s broker (or if it is unknown as to whether or not the listing office offering compensation), then the buyer can use the purchase agreement to ask that the seller contribute something toward the buyer’s obligation to compensate their broker.