They will give the standbys Comfort+ seats before they move passengers not eligible for an upgrade to Comfort+. This is mostly since it's a bad customer experience to unilaterally move a customer's seat (they might be sitting next to another passenger on a different PNR) and at the time the standby list is cleared, the gate agent doesn't have time to call people up and ask. Delta employee non-revs are also eligible to be seated in the highest cabin with available seats once all revenue customers are accommodated, which in many cases will be Comfort+.