I am NO expert, but I can share that I keep one or two potted plants in the enclosures for all of my snakes. I have had really good success with Pothos and Snake Plants. Most of these plants have been thriving for at least a couple of years; they seem to appreciate the humidity - most of my snakes are kept at about 60-65% humidity - and a few hours a day of LED lighting (though I do have Jungle Dawn UVB lighting in several enclosures). I just keep a standard plant saucer under each of them. I use pretty deep substrate in order to maintain humidity and because many of my snakes like to burrow - so I cover the saucers with substrate. I wrap fake vines around the planters because even if my snakes don't care, I like an aesthetically pleasing enclosure.
hihit is right about Aloe - I wouldn't use it for most of my guys, but it does really well in my Sand Boa enclosures.
I have been (still am, really) VERY cautious and honestly a bit cynical about the current fad of bioactive keeping, though I won't get into that particular rant here. I do think bioactive is a good idea, and maybe even the best idea, for small animals like Dart Frogs and most of the popular geckos. But I'd still need to be convinced with better information than 'It's cool' about how and why bioactive is really any better than a good naturalistic setup for most snakes.
I'm coming around to greater acceptance of well-researched bioactive in specific circumstances, though, and am likely going to cave in and try it for a couple of my crew. We'll see. I'll post if I am crazy enough to give it a shot.
Editing to add: if you do end up fighting fungus gnats, I can recommend a 'Katchy' bug trap. Check them out on Amazon. They're pet-safe, not bad-looking in the room, great for fruit flies and gnats, and a real blessing during mosquito season as well.