Using additional cameras in ARKit - are there any resources to show how this is setup?
ARKit allows streaming video from only one camera at a time. Which camera is used is determined by your configuration (e.g. ARFaceTrackingConfiguration will use the front facing camera, ARWorldTrackingConfiguration will use the back wide camera).
You can, however, enable face anchors detected by the front camera in an ARWorldTrackingConfiguration with userFaceTrackingEnabled. Vice versa, you can enable isWorldTrackingEnabled in an ARFaceTrackingConfiguration to benefit from 6DOF world tracking.
Check out this developer sample: