That seems to be a stretch. They filed for divorce in 2002 but were having problems almost right away, according to the article in Oregon Live, after marrying in 2000. It states the step-mom began a relationship with the dad after the step-mom moved in to care for Kyron in 2004.
http://www.oregonlive.com/portland/index.ssf/2010/06/kyron_hormans_blended_family_f.html
Plus, from everything we see, these people, in the most stressful of circumstances, are supporting each other. Their conduct supports the article. I would have no problem with a friend dating my ex, depending on the situation. It seems the mom and dad were not a good fit and knew that very quickly. But, the step-mom and dad are. So what? These people seem very mature and how they have helped each other to raise Kyron. In my business (divorce/custody), these people are rare jewels. If more people could ignore their petty jealousies and immaturity to work for the best interest if their children, the world would be a better place.
I'd rather have my best friend raising my kid than a stranger.
There are strange things about this case and some questions but I really think some of us are trying to make the facts fit our beliefs about the case. That kind of makes me feel icky.