I don't think you can reproach anyone for not being a hero, and especially for not "owning up" to crimes they never committed. That said, I just listened to that poem and it appears to be a stab at Russian antisemitism much more than at Nazis. I believe by the 60s antisemitism was already an unofficial government policy in the USSR, so he's in no way beating an officially designated dead horse. Pretty sure publicly mentioning Katyn at that time and place would have been suicidal.