Genetically modified salt vampires, designated Species M-113, are featured in a zombie-like invasion of a Romulan mining colony in the Hfihar system, in Star Trek Online, since Season 8.
One of the endgame body armors in STO was originally going to be called Kellerun. Didn't happen, though. Aside from that I can't think of any further reference to the Kelleruns, T'Lani or harvesters. Maybe Miles's coffee habits?
The Best of Both Worlds is never mentioned again. EVER. In seriousness, my guess would be some one-off alien-of the week episode of Voyager. It's harder to reuse or namedrop a race in another series's novels when they're off in an entirely different portion of the galaxy.
I've got the ultimate contender! VOY: Living Witness Because it is set in the 31st century and beyond on a world without further contact with the Federation, nobody is going to revisit it in our current timeline. The only references I could think would be sth. like a Kyrian Starfleet officer from the far future in a DTI incident or, more likely, Warship Voyager becoming playable in STO. Unless there's another short story about it...
^Sorry, but there's a terrific Strange New Worlds IV story, "Personal Log" by Kevin Killiany, that's a direct sequel to "Living Witness" told from the backup EMH's POV.
I was 'afraid' Strange New Worlds would strike again. There has to be some unreferenced episode, after all.
It introduced Kathryn's Gothic holonovel, I'm not sure whether that counts. But as posted above, VOY episodes are most likely, in general.
Has there been any reference to the episode "Paradise" from DS9? If there is, I bet it's in Strange New Worlds or something.
In Keith R.A. DeCandido's Enterprises of Great Pitch and Moment, Sisko tells Picard about Alixus trying to destroy the runabout.
Actually, I just thought of another "Man Trap" reference: back in the 1970s, there were a number of whimsically illustrated Star Trek "NO SMOKING" signs in (I believe) the Lincoln Enterprises catalog. One of them was "Smokers will be introduced to the Salt Vampire." (Another one, with a picture of NOMAD zapping somebody, declared that "Smokers will be sterilized.")
Memory Beta has Zalkonians listed in the "species" section of Q-Space's reference sections. http://memory-beta.wikia.com/wiki/Q-Space