I didn't quite understand the question. An REO is now listed with a real estate agent and you want to make an offer on it with your buyer?
If you have a purchase agreement accepted on the property it is not with the agent, it is with the Seller (REO owner/bank whatever the entity might be, who knows anymore).
While the property is active as a listing, the agent has a duty to the seller to make it available for showing to buyers via licensed real estate agents, only licensed real estate agents (CA), can talk specifics about listed real estate (the law).
Then the terms of the purchase agreement come into play... the buyer's access or lack of access thereof are determined by what was agreed upon in the purchase agreement. The window of time for the inspections, appraisal contingency (if any), etc., everything is negotiable (almost everything) and once you have a fully executed purchase agreement, then the parties must follow what they have agreed upon. The licensed real estate agents have a duty to make sure the parties rights are adhered to.
The Listing Agent isn't subject to another commission, they have the contractual right to it, if it is so stated in the Seller signed Listing Agreement and they double end the transaction (represent both buyer and seller = dual agency, which can be very dangerous in a litigious society- but hey, liars need to earn a living too!)
Hope that I answered your Q okay.
Good Luck! -- Dawn