Alright, I have a lot to cover here and not a lot of time so I am just going to dive in and I apologize in advance if I come off terse
I don't believe U. longifolia requires a dormancy period to survive long term.
You are correct, it does not.
The dormancy is required for flowers.
In some cases yes in others no. There are at least 4 distinct clones of this species in cultivation. One clone (var. forgettiana) is very free blooming and does not require a rest phase (I do not like the term dormancy cause the plants are never in a state of inactive growth, just slowed growth.) Two of the remaining clones do require this rest phase to consistently flower and the last one is squirrelly, behaving differently in different peoples collections.
The only problem I see you having with growing a Heli with U. longifolia is that the U. longifolia will take over and fill the pot. This may or may not have an impact on the Heli.
This will not be much of a problem
You also may never be able to completely separate the Utric from the Heli when it's time to repot.
If the goal is to grow them together I doubt this will be a problem either
Yes it would be plenty moist enough for the U. longifolia. I always describe watering this Utric like a Nepenthes, which is moist but not soggy. It can survive in a variety of media types. I have found that for me, in my conditions, it grows best in a mix much like you describe with orchid bark, LFS, maybe some perlite and cypress mulch thrown in. I also have some growing in a peat and sand mix. It seems to grow faster in a more open mix like mentioned above (for me).
Again, this is going to depend on the clone. Each one seems to have a pretty broad range of tolerances and, while there is a large area of overlap between them all there are still outlier conditions. For example, one clone will happily grow fully submerged while another will rot out under those same conditoins.
WHAT?
It is absolutely not necessary for flowers. At least for my clone.
As I said above, this depends on the clone.
But U. nelumbifolia goes really well with helis. I've actually got one with it's tendrils in a helis pitchers, without my help! The tendrils are starting new plants in the heli.. kinda cool.
Just an FYI, plants growing in Heli pitchers are significantly weaker than those under other conditions. Seems something in the Heli is a bit detrimental
Btw, this utric loves it soggy. It can tolerate dry, but it grows much faster flooded, then drying out a little.
Again, this depends on the clone. I would avoid making such sweeping statements. It just gets people into trouble
Many people are just realizing some of these macro utrics can take a lot wetter conditions than people generally expect.
Here's my proof:
Remember that U. longifolia is wholly unrelated to the rest of the "macro" Utrics. What it can tolerate and what the Orchidioides and Iperua can tolerate are not the same thing. The only Iperua that is as tolerant as longifolia is nephropylla.
Maybe keep the heli all by its self as a focal and plant the U. humboldtii in a nice Broncchinia (i know this happens in the wild, a la Barry Rice's book?)?
U. humbo does not really do well in bromeliads. Yes, it will grow in them but it does much better when grown terrestrial.
Obregon - I have looked all over the internet for U humboltii (for my personal collection) to no avail. They seem to be available everywhere but the US.
They are here in the States, you just have to hunt.
I believe that U. humboltii and U. quelchii(?) are the only Utrics that I have made a positive connection to Helis in the wild.
Not quelchii, it really cannot tolerate overly wet conditions. The bromeliad associated Utrics are mostly humbo and nelumbi though reni have also been found in them on rare occasions
And, just a quick answer for you. Atlanta Botanical has U. longi growing in among the Helies in the highland display greenhouse so you should be fine having the two together in your set up.