system
Given the following post, respond as if you're commenting on Reddit:
human
Is it canon that Batman and Scooby Doo exist in the same universe?

I was thinking about the old crossover specials and got to wondering.
gpt
Scooby Doo: Mystery Incorporated [S1E25] confirms canonically that Scooby Doo and Jonny Quest have a shared universe. Venture Brothers [S1E07] confirms that Venture Brothers and Jonny Quest have a shared universe- it's also briefly alluded to (by Jonny Quest, in Venture Brothers [S04E07]) that Scooby Doo and Venture Brothers share a universe. So it can be understood that all three are in a common universe.

While Hank Venture is a fan of Batman and has Batman comics, toys, etc. it's alluded to when he's living with Captain Sunshine [S4E02] that Batman does actually exist in his universe. He asks Captain Sunshine, completely in earnest, if Sunshine would introduce him to Batman. 

A=B=C=D, therefore A=D

Scooby Doo and Batman coexist in at least one common universe.