They're not technically monsters. One haunt allowed the traitor to move them "up to their speed". In that case and other similar ones, are inhabitants hindered by general obstacles? Can heroes be obstacles to inhabitants that are obviously working against the heroes?
According to the rulebook:
MOVING PAST OPPONENTS
After the haunt starts, opponents act as small
obstacles. Heroes are opponents to the traitor and
monsters, and vice versa.
While Inhabitants are not directly mentioned here (as they aren't in the base rulebook until the sticker is added), if they are actively working against the heroes I would count them as "opponents", thus heroes should be obstacles to them. However, I think I would go along with Chris' reply above and assume the Haunt will specify whenever this is the case.