Can music files exported from rekordbox (Mac/Windows) to a USB device be played on this unit (the XDJ-AERO)?

Yes they can.
When the USB device onto which the music files were exported from rekordbox (Mac/Windows) is connected to this unit, tracks can be selected while browsing them by category (titles, artists, etc.). Playlists created with rekordbox (Mac/Windows) can also be used.