Working in the haunt industry and being trained by some of the awesome heavy hitters throughout the Ohio Haunters Association, I can say that roamers are good to have. At an outdoor attraction, such as KI, to get people amped up to enter the house (maze) or scare zone, you want to have queue actors (aka roamers at KI). Imagine going to a haunted house in the middle of October and there is nothing outside of the house to set the mood that you may get scared including actors. You just walk up to the building and enter with no "setting" being portrayed, no actors giving you information on the place whether rules/history/portraying a character that may be inside...it'd be boring for sure. If they half @** or not even that, the entrance experience you'd likely expect the inside of the attraction to be half @**ed.
The queue actors not only amp guests up to head into an attraction, but they set the expectations of how to act within the attractions. Yes you have your greeters at the entrances of the mazes for the rules but in person interactions when a guest touches what they shouldn't touch (actor or prop) queue actors have more flexibility to roam, tell a guest to stop, flag security down, etc.
I have not worked a Cedar Fair haunt, but I will say that I do know the haunt industry is way more complicated than what meets the eye.