We had a long thread going on the Collector's Society Forum about both Dreamwalker 0 and Avatar Illustrated 1998, with one member asking Powell directly when meeting him at Dragon Con 2009.Both books contain preview material of content that had already been created with the intent it be in Goon 1 Avatar Press. So supposedly, these books ARE NOT the 1st appearance of the Goon, but rather preview material.
You are right on the reprint of Dreamwalker 0, as Jenni Gregory continued to reprint her material under the Dreamwalker 0 title, but this does not contain the preview Goon material. You can easily tell the difference in that the original issue was published by Avatar Press, and her reprint version is published under the Dreamwalker Press banner.