I don't know how this is possible, but I have the following growing next to each other in the same terrarium successfully:
Sarracenia purpurea venosa
Nepenthes ampullaria
Heliamphora minor
Cephalotus
All of them are producing healthy, colorful traps. They are also growing quite quickly too. Well, except for my Cephalotus. I repotted it in fresh soil about two weeks ago and it went into a bit of suspended animation. But now it's starting to grow again (I see the fuzzy grow center sending out new leaves)
now that's a new one... That just doesn't seem at all possible, but if it's working, awesome! The only thing I can think of as far as the plants not doing well is the sarracenia. It may not show any damage and could very well be growing very quickly as well as have very good coloring on it's pitchers, but if it isn't allowed to go dormant in the winters, its lifespan could potentially be shortened. Other than that, I don't see anything else that may be suffering while you can't see any effects. That just seems weird that you're able to grow plants that come from such different climates together, and have them all be healthy, but if you're doing it, then great!
Anyways, onto my experience with growing cephs and Helis together...
I don't have too much experience in growing either of these plants, compared to some people on the forum, but I have been growing a Cephalotus Follicularis alongside multiple Heliamphora species, with pretty good results. The Helis I've grown the ceph with, have included Minor, Heterodoxa, Pulchella, Nutans, and Heterodoxa x. Minor. The conditions that I grow mine under are as follows:
Daytime Temp. 75-80F
Nighttime Temp. 65-70F with some nights down closer to 60F
Humidity 70-75% during the day and about 80-85% at night
I have a simple shoplight for lighting, 2 T8 or T5 bulbs (I'll have to check which), each bulb is a 32W "soft white" bulb. I also have a plain old 60W compact fluorescent bulb angled into the terrarium, so that it casts it's light in a wide and even distribution, on most of the plants, which includes my Helis and cephs. I have a humidifier that runs 30min before the lights come on, all day while they're on, and then it turns of 30min after the lights go off. It then comes back on again at 12:00am and 3:30am, for 5min each time. I don't have any cooling fans, but I have lots of air movement in the room with the terrarium, which is provided by a rotating floor fan. I am going to be adding 2 small computer fans so that the ventilation is better in the terrarium, because there is algae starting to grow on the surface of the pots. I figure that if the fans take out enough humidity to really change anything, I can always add more with the humidifier, but if I am not getting enough air circulation, then something needs to be done, hence the fans.
So far, under these growing conditions my ceph is looking very nice, it's still pretty young, so it hasn't developed full colors, but it is a nice green color with some nice darker areas, as well as some nice reds mixed in. The Helis that have been grown with it all seemed to grow pretty well, not as good of color as, for example Butch's Helis, but I only know a few people who can really even come close to his Helis as far as color. All of the Helis grow at a normal growth rate for their species, and have pretty good colors, very nice, soft greens, with some great reds in the mature plants. I did notice that the Helis were a little bit less good looking w hen they had somewhat warmer nights, ~70F, and a little bit lower humidity, 55-65%. After making some changes to my growing area and techniques, they seem to be doing better. I would post pics, but right now my only Helis are divisions that were divided very recently, so they don't look as nice as they otherwise might. My ceph is looking really nice, and I'm actually getting two more, Hummers Giant and Vigorous Clumping, so I'll post pics of those tomorrow, after they arrive. As always, if you have any questions about how I set things up for my terrarium, or about anything, feel free to ask, I'd be glad to share...I don't have too many dark secrets