iPad and Tracktor

Quick answers:

S4/S2 MK2 do work with iPad (Traktor DJ)

Z1 is quite a strange case: it is fully working (audio interface + controller) on iPads with lightning, but it is working only as controller with IPads with USB C. At least older Z1 model that used to have also a power connector. It has been removed on newer version.

X1 does not work with iPad, being it not class compliant.

Have a look at these articles to have a better idea

https://support.native-instruments.com/hc/en-us/articles/210280705-How-to-Connect-your-NI-Controller-Audio-Interface-to-an-iOS-Device

https://support.native-instruments.com/hc/en-us/articles/210271805-TRAKTOR-DJ-iOS-Audio-Interface-Compatibility

EDIT Correction: I found now a video of a guy making the new version of Z1 work also as an audio interface with an USB C iPad with Traktor DJ 1. Therefore I made some more testing: I don’t know why, but I can’t manage to make my original Z1 work with my M1 iPad 12.9 (USB C) as an audio interface. As soon as I plug it to my iPad Pro with lightning, everything works: controller and audio interface

And they should work with DJAY (of course in midi mode)