OK, you might want to pin this topic for future mac users who buy the VMS4 and Traktor Pro.
I've managed to work out the settings to use the VMS4 with Traktor Pro with 4 decks.
Midilog 1 is Deck C
Midilog 2 is Deck A
Midilog 3 is Deck B
Midilog 4 is Deck D
In your output settings, select as this:
Output channel A = Back Left, Back Right
Output channel B = Front left of center, Front right of center
Output channel C = Front left, Front Right
Output channel D = Side left, Side right.
ENJOY!