Ramp Tramp. Yep, thanks. Class 6 CAO in the belly?
As a practical matter, we do generally have all DG accessible. Apart from anything else, its easier to account for.
We'll take DG/PAX in the lowerdecks if there's no other way around it. This is a rare enough occurence, with the exception of cars. Class 7 into the rear belly, size/weight permitting.
Airlines do make up their own more restrictive rules. Have a look at Operator Variations towards the front of IATA DGR.