First I must point out that I’m extremely new to Maya, I’m only using it for the ART tool. That might be part of my problem. 
Question:
It seems the ART Rig export is missing the constrain settings that I added to deformation helpers
(knees, elbows etc.).
The constrain settings are still there, in Attribute Editor/Extra Attributes. They are just not working for some reason?
The Export file is fine, when reimporting using Edit Existing Char.
FBX exports are also behaving as intended.
For deformation helper bones I used leaf joints.
Request:
It would be great to have orientation constrain and point at constrain joints added to the Add Rig Modules section. 
On the Export File the knee and buttocks are behaving nicely with correct orientation blend:
On the Rig File the deformation joints are not blended between the the parent bones:
