As Jobi said, there are monitors that nest in the ground and monitors that cannot because the ground is not suitable.
Forgive me as I did not read this post that closely. But in your first post you mention indo and aboreal.
First, monitors that are aboreal are not restricted to indo, and not all indo monitors nest in what you think as aboreal areas.
Most of the indo species I worked with nested in the ground, but dirt is not a perferred nesting material.
Which brings up another point, what the heck is aboreal? Specially when you consider, most cages are in a house, and houses have 8 foot ceilings. As far as aboreal is concerned, 8 foot is the bottom of a tree not aboreal.
Now within that distance, that 8 foot, how does a monitor know what is aboreal and what is subterrainin?? I mean, if you have a tall cage on the first floor of a building, is that aboreal, or if you have a short cage and you live on the tenth floor of an apartment building? Is that aboreal.
Would argus not nest by burrowing down in the dirt, when on the tenth floor of a building?
What I am getting at is, aboreal is a, I am trying to be nice here, not very smart concept when you have cages less then 15 feet tall. As I have said before, I have seen all sorts of teresterial monitors in short trees, including ackies(about 15 feet up)
So back to Jobis comment, I think its more important to think of nesting in terms of suitable big enough conditions, then whether its off the bottom of a cage or not.
Truthfully, I do not think the monitors are confused by this, only people. A monitor knows what up is and knows what down is, and surely knows that 8 foot is not up. They also know what is suitable. Cheers FR