If you haven't seen articles, Monster Mansion/Plantation was designed by an ex-Disney imagineer. While I haven't riden it yet (I've been wanting to for years), based on what I've heard and pictures I've seen, I imagine it has many Disney-esque touches.
I believe it's Six Flags Over Texas that also has a dark ride, a boat ride featuring Yosmite Sam and the rest of the Looney Tunes cast. So dark rides at Six Flags are not unheard of. Wish they would do more of them!