Whichever way it’s done, it most likely will require a sync operation EVERY TIME you change something on another platform.
Let’s say you have all your stuff on Traktor, then you transfer it all to your RB stick for use in a club. While playing CDJs, you add a few cue points, a loop or two. Also you change a typo in a track title and correct a 78 bpm into 156. This information will be available as you read your USB stick back into your computer RekordBox. Now you have to sync that information back into your Traktor. You buy a few new tracks, prep them and all and sync all that stuff back over to RB.
Also I doubt, but I have to yet watch the full video, that RekordBox will just take over the beatgrid that Traktor provides or vice versa and highly unlikely whatever information you added to it (like drop beat).