Most of the null-crossovers I've examined here have been covers or one-page interactions of characters that are not genuine narratives, like this one. SECRETS OF HAUNTED HOUSE #44 is a crossover between various horror-hosts, consisting of two pages at the comic's beginning and a full-page joke at the end. Despite the greater length I would still judge this to be a non-narrative vignette of the type I discussed here.
As usual in these types of vignettes, the hosts not only don't interact with the characters, there's also no real narrative in their three pages here. This is in marked contrast to the EC story "Horror Beneath the Streets," examined here, in which the hosts both interact with their "victims" and dominate the story as focal icons.
As a curiosity, the letters-page issue of HOUSE also sports a "crossover" of a very different sort, as future comics superstar Todd MacFarlane weighs in with his opinion on a recent issue.
The same lettercol includes a separate letter in which a fan asks about the disposition of several DC characters that have nothing whatever to do with any of the horror-titles. I rather doubt the fan directed this inquiry to SECRETS OF HAUNTED HOUSE; probably someone just wanted to run the letter some place and SECRETS had a hole to fill. This exchange is amusing for a comment, attributed to DC editor Len Wein, in which the reader asks about the TEEN TITANS character "Bumblebee" and is told that the character "never existed."