The box set features WB logos and small print specifying a 1987 copyright renewal, so
House on Haunted Hill was definitely licensed through WB. As I recall, WB
would actually license individual titles, on occasion, for inclusion in other companies' box sets, where appropriate.
See also: The theatrical cut of
Nightbreed for the
Limited Edition release and
True Romance for
Tarantino XX (both of which are no longer with WB as their own license with Morgan Creek has since expired). I think there was another example or two, but I don't recall which set(s).