The last I heard about this was from their own communication:
Facebook has never had a server to server integration with any of the major DMP players, but DMP customers have been able to send audiences created in the DMP to Facebook via Facebook’s Web Custom Audiences (WCA) feature.
From Adobe’s perspective, it is up to the customer to decide how and when Web Custom Audiences are used on their site; this may include leveraging Web Custom Audiences with Adobe Audience Manager pixel based destination so long as this is done in a compliant manner. It is important to note that both Audience Manager URL Destinations and WCA are self-service offerings managed by the customer.