my U. campbelliana was a times growing under water. Leafy stolons all submerged.I think this tub is a special case. Over the years I noticed that U. reniformis acted like U. longifolia in that, soon after potting, new rolons would pop out the bottom holes. U. longifolia loves living in the water saucer. With the similarities and the fact that U. reniformis has those large swollen pain-in-the-butt rolons - it made sense to try a tray/tub. The blooming all summer on the windowsill was a really pleasant unexpected gift.
In general, I dislike having pots sitting in water. It's conducive to anaerobic conditions (depending on media & environment) & I have a somewhat irrational distaste for that state. However, if a plant continually shows a desire for those conditions, it would be silly for me to ignore their wishes. Most of the original Orchidioides (not including Iperua) seem to detest a no-oxygen media. Success with U. campbelliana & jamesoniana sitting in water (as seen in Mach's post above & my treefern & hygrolon plaques) doesn't seem to be an exception since the open/airy plaques don't develop anaerobic conditions - probably similar to the sponges in your post.
In the future, I hope to have an environment with automatic misting/sprinkling so there would be no need to sit the epiphytes in water.
**Edit** After I closed this post, I looked at my windowsill. In addition to the large reniformis which I will soon be adding, there is a small container of U. geminiloba that I added last January. Since I knew it wouldn't handle the super-low household humidity in the winter (at least w/o acclimation), I placed a small division in a takeout clamshell container. When summer rolled around, I opened the clamshell to keep from creating a solar oven. Although I can't say it has 'taken off' with growth, the division has increased steadily in size - it now has 1" leaves on 2.5" petioles. This is still much smaller than my basement plant but since the basement plant has never flowered for me - I needed to try something (hey it worked with reniformis...!).