The only reason the AL-KO AKS hitch head needs a matching towball is because it has more clearance and is machined underneath to be a bit taller.
Anyway, even using an AKS hitch on a non AL-KO ball would not let it unhitch itself. It would only be at risk of damage and poor articulation in extreme circumstances.
Just because it was showing as "green" does not necessarily mean it was correctly hitched. It is very easy to get a mis-hitch, one of my major gripes with the AL-KO system. The Winterhoff is vastly superior IMHO since the stabiliser part cannot be engaged unless the hitch is correctly located on the towball. Anyway, I digress.
I find the best way of hitching the AL-KO is to test it by trying to lift it off with the jockey wheel after it has locked. Yes, it's a pain and yes, I consider it essential for peace of mind with this less than perfect system. In an ideal world the Winterhoff hitch head would fit the AL-KO chassis.
As regards the matter of the van not pulling up straight, things like loading and road surface all have a bearing on this. In a car we have the steering wheel to prevent this.
Dom.