You are right, most Zattsu artwork, either the original cute ones or the violent edits, is not labeled as 'zattsu', just the zattsu-hater drawings. I don't know why they are not labeled with his name, maybe the labeling could lead to a knee-jerk reaction leading to add a 'deletion_request' tag to every artwork labeled as 'zattsu'.
^ Unfortunately, this site isn't like danbooru (artist tags have a different font color) so I suggest an initiative to use a distinct marker (a bracket or anything) for tags that refer to artists.