Fantastic encosures and ackies!
I had the impression that they used more the floor than the high, but it´s nice to see them in the higher shelves.
As regards the plants, I would suggest pothos (scindapsum). I have been using them for years with several species of snakes (mostly Morelia) and they survive.
Monitors aren´t snakes, of course, but I think with the ackies, you could try some pots hanging from the ceiling of the enclosures (one in each corner). It would look great with the leaves hanging towards the floor. As long as the pot itself is "ackie safe", the leaves would come and go without issues to the plant