The Crossover UniverseTM is a companion blog to the books Crossovers: A Secret Chronology of the World Volumes 1-2 by Win Scott Eckert, and the forthcoming Crossovers Expanded Volumes 1-2 by Sean Levin. Material excerpted from Crossovers Volumes 1 & 2 is © copyright 2010-2014 by Win Scott Eckert. All rights reserved. Material excerpted from Crossovers Expanded Volumes 1 & 2 is © copyright 2014-present by Sean Levin. All rights reserved.
I haven't read this. So is Groo in the CU? Or is it an AU or what?
I'd say he's in the CU based on this, though the framing sequences involving Mark Evanier and Sergio Aragones would have to be in an AU. The Groo stories take place in an unspecified distant past that could be the Hyborian Age.
The Groo comic was comedic so it could be an exaggerated version of the Hyborian Age.Groo appeared at least once in the background of a Usagi Yojimbo comic. Which is interesting since most of the characters in Usagi are talking animals.