according to the manual, Havent seen it in a video yet though, You can plug in a loaded usb drive, then connect the iPhone wirelessly to view and load the tracks that are on the usb drive
from the manual:
Loading tracks from mobile devices or computers via wireless LAN
1 Connect the mobile device or computer to this unit via wireless LAN.
2 Launch rekordbox on the mobile device or computer and establish the link.
3 Operate rekordbox on the mobile device or computer to select the track.
4 Operate rekordbox on the mobile device or computer to select the deck on which the track is to be loaded, then tap or click.