Well here's my take on side exit exhausts:
There's nothing mentioned for MA category vehicles in the ADRs. In NSW, there's nothing mentioned for MA category vehicles in the NSW specific legislation either. Across Australia, this MC category vehicle is sold with sidepipes:
Road Vehicle Descriptor (RVD1)
Mercedes-Benz Australia - Facts & Figures - G 55 AMG
and to quote from the advertising:
"...an AMG exhaust system with chrome-finish twin tailpipes on each side of the vehicle..."
you can even see them in the photo montage on the website. They are for sale, and sold as is listed in NSW - there is one here in Orange in this specification.
It is a category MC vehicle, which means different requirements under the ADR, but a 5.5 V8 and sidepipes, in a 4WD is as far as I'm concerned, equivalent in behaviour to a passenger car.
Treeve