tow hitches

Just ask them wheer they get them done. Generally they farm out fitment to after market stores so you will probably get a Hayman Reece bar anyway.
If not, just get it written into the sale that you want one. Saves you running around and as it was fitted at time of delivery, you should get dealer backyup is something like the electrical work fails.

Doesn't really matter much as long as it is professionally fitted and is rated to suit the load you wish to tow. ADR62 requires all towbars to have their rated capacity stamped on the bar. I suppose if you get the dealer to fit it the General would not be able to use the after market bar as a warranty loophole should something remotely related to the towbar occur but you are gunna pay for that because they make a profit on all accessories they fit. Compared to the vehicle price + GST + Stamp Duty, etc that could be a small price" to pay.

If thats who you are picking between I would go for the dealer ARB are so hopeless they would probably fit it to the front

The factory towbar fitted to the RA's 03-pre RA07 had the hole in the receiver and hitch slightly offset. The ofical reason given is that you could not then fit an inferrior (less than 2000kg) hitch into the receiver.
The downside to this of course is that the hitch then cannot be inverted to suit the trailer, and most other COTS hitches can't be used. This also makes it a pain if you need to swap between 50mm ball, treg hitch or pintle hook.
My 03 RA has the factory towbar and has the offset hole, my 05 RA has a Hayman Reece towbar. Both towbars were ordered as part of delivery, but at two different GMH dealers.
I don't know if the RA07 factory towbar continues with the offset hitch or not, the TD manual has an increase of 1t to 3t towing capacity now.

Cheers,
Dion.

p.s. when I put the Kaymar bar onto the rear of my 05 RA, I will have a Hayman Reece towbar for sale, but it will even if bolted to a 08 RA will be limited to 2t despite the 08 RA having a 3t towing capacity.