Yeah...I'm not exactly sure I'd call this a dream match when you consider a couple of important factors.
1. DDP, Scott Hall, & Jake The Snake Roberts are 57, 58 and 58 years old. That's a combined age of 175.
2. Hall & Roberts have had major health issues over the years and that's not even counting the many decades they've battled substance abuse. Frankly, I doubt either Hall or Roberts are remotely healthy enough to compete. You know that WWE would want to protect them and its own collective ass, which means they'd put them through a barrage of medical tests & exams. I'd say that DDP would have no problem as he's someone that lives and has lived a very healthy lifestyle, but the same can't be said for Hall and Roberts.
I understand that people can be nostalgic about wrestlers they grew up watching. I'm the same way, nothin' wrong with it. But there's a big difference between being nostalgic and letting nostalgia blind you to the truth. I think it'd be a great moment to see Scott Hall & Jake Roberts appear in a WWE ring, Roberts especially, but not as wrestlers and especially not at WrestleMania.
Even if the match took place, what exactly is the benefit aside from some major marks of these guys getting a bit of a thrill? Beating or getting beaten by a trio of senior citizens won't exactly do much to elevate The Wyatt Family. I could see Roberts in the role of a mentor to Bray Wyatt, maybe even something of a father figure. You know, the man who showed Wyatt what "the truth" truly is and set his feet on the path of knowledge.