Official comment
Yes, the Facebook Custom Audiences integration will now show all of your Ads Manager or the Business Manager account for your Facebook account. In addition, after you have your Facebook Custom Audiences set up, connecting ONTRAPORT to your Facebook account is a simple affair; simply click your Profile icon, then Administration > Social and click the Facebook API icon. Click on the Continue with Facebook button and allow the pop up. Log into your Facebook account in the pop up and that's it ... ONTRAPORT is now connected to your Facebook account via their API, and you can add or delete contacts from the Custom Audiences using any of the ONTRAPORT tools.
See our Facebook Custom Audiences article for more details.