I exported tracks of iTunes Playlist to USB/SD device using rekordbox ver. 5, then edited the track data (cues, beatgrid, ratings) on a DJ player. Can I use [Update Collection] of rekordbox ver. 6 to get the edited track data back to my collection?

You cannot use [Update Collection] of ver. 6 for the tracks exported using ver. 5 (iTunes Playlist).

Please perform [Update Collection] on ver. 5 before using them on ver. 6.