I'm reluctant to definitively state that this is a violation, but that information really should be available in some form or another. I think there are lots of ways that could be done; for example, it would probably be fine if the history section of the final article had a link to the history section of the article that was merged in.
In other words, we should merge and redirect, not merge and delete, which is exactly what we do. It would seem our understanding of the GDFL is correct (in that aspect, at least).