I didn't really have anything much good for the idea seed itself of Cenobite Scooby-Doo. Being disinterested in Hell Raiser, I kind of went in a similar direction to what was on the show referred to (awesomely) as "Scooby-Doo in the Vineyard," only with a lot less in the way of details. I kind of got hung up on the Cadfael mysteries, although I'm pretty sure he didn't belong to a Cenobite order.
However, a stray remark in the actual show sparked something Scooby-Doo-ish, but completely non-Cenobite. Ben (I think) started talking about all the things that Velma, Daphne, and Fred must be doing while Shaggy and Scooby are getting chased around, and it kind of sparked something similar to some of the results from the "Bond Behind the Scenes" show (oooh, episode cross-over
Anyway, the thought is that this isn't just an accident. Shaggy and Scooby are the distraction.
It's they're job to convince Mr. Johnson that the hoax is working on the newcomers. You could run this two ways. The thought that the others are taking advantage of Shaggy and Scooby's natural cowardice and gullibility is just kind of depressing, so I started going in the direction that they know it's their role, and all the running around and screaming is part of the act.
But everything we see of the gang shows Shaggy and Scooby as a couple of cowardly, food-obsessed dopes. If that's an act, they're putting it on even before the gang "discovers" that there's something strange going on. This in turn suggests that they're not just happening on these places because they're visiting a relative or an old friend, or just taking a driving tour of creepy old towns. The whole thing starts to look proactive.
At this point it became impossible to not be tempted by Scooby-Doo Leverage.
Velma is clearly the Mastermind. Unfortunately, the rest of the gang doesn't fit quite so neatly into the archetypes. I've got some ideas, but they require you to squint a bit to work.
Scooby seems to frequently "accidentally" do something that knocks over the monster and buries it under a bunch of old tires or something. Conclusion: Scooby is the Hitter.
Shaggy is the Grifter. This fits in with the entire distraction part, and he's more verbal than Scooby.
I'm leaning toward Fred being the Hacker. If I recall, he's the one that often comes out with the various bits of background knowledge and figures out how the hoax devices actually work.
That leaves Daphne as the thief. That kind of works with the whole Danger-prone Daphne bit, if you think that instead of accidentally falling down the trap door or getting caught behind the sliding panel, she's triggering them on purpose (and possibly going off the rails in a manner similar to Parker in the Leverage TV series).
"The rich and powerful dress up as monsters and take what they want. We pull off the rubber mask and steal it back for you."