I don't think the rumor is that far-fetched. While the event is not exactly the same from park to park, many Cedar Fair parks share the same mazes/themes/names/scare zones during their haunt events, and I believe Six Flags does the same. That way corporate only has to come up with one idea and test it out at one park. If it works, mass-produce the idea and ship it out for each park to implement in a
similar way. This isn't to say every SEAS park needs to have an event that's the spitting image of its sister parks. Each event could/should maintain individuality based on the say of their own management, but this would save the company lots of money on branding, creative design, technical design, etc.
Better yet, design the mazes to be easy to pick up and move. That way every few years each park can just pack up their mazes and rotate them throughout the chain, bringing a new set to each park every season or so.
They could probably pull it off because the SEAS parks are fairly spread out, and
most people probably don't make it to more than one SEAS park within the Halloween season anyway.
Edit: By the time I finished typing this, a bunch of posts had already been made on the subject. I like Party Rocker's idea of a corporate Howl-O-Scream team, though. It's like what Cedar Fair does: downsize each park's individual haunt teams and have everything come from corporate, thus cutting costs and perhaps bringing about more consistent events across the board.
Edit #2: Seaworld-related paragraph deleted thanks to a correction by Party Rocker.