epiphyte mats in tropical forests
Adventitious roots into epiphyte mats aren't all that uncommon, and aren't restricted to the tropics. They can occur in old growth forests in the pacific northwest (my neck of the woods). A well-developed bryophyte mat in a single upper canopy tree can store up to six metric tons of water, plus all the mineral nutrients from atmospheric deposition. For the tree, it's a huge advantage to be able to tap into that epiphyte mat rather than rely on bringing up water from their subterranean roots. As far as visualizing it goes, yes, you would have to remove the mat to see them, but they look very similar to subterranean roots. Not sure if this is helpful, but I like to think of it like this: when a new meristem is formed, it's basically undifferentiated, and if there's sufficient water and mineral nutrition it can develop into a root (or a shoot if it's getting sunlight). The tree doesn't care if that's below ground or in the canopy.