Generally GMCL is pretty trusted. However, there's only one other Japanese site that mentions the alias, so I'm not sure where to go with this. Some corroborating evidence is that the dates don't overlap, implying an official change in what he wanted to be called (although he mostly used NON.) However, I can find some places where he's still credited as Kazuo as late as 1997:
http://www.jbook.co.jp/p/p.aspx/7152/s
Assuming they are the same person, I don't think it's clear which is the real name.