No.
The issue wasn't that he brought up Hitler. The issue was that he (basically) said that even Hitler wasn't as bad as Assad. The comment about Hitler not using chemical weapons was his mistake. Had he simply said, "Assad is as evil as Hitler", or something along those lines, I doubt it would have been more than a blip on anyone's radar.
The issue is not mentioning Hitler's name. The issue is that it appears he either doesn't know what happened in concentration camps, doesn't believe it happened, or was too stupid to make the connection that Zyklon B= chemical weapon. If you saw his response, when the ABC reporter asked him to clarify, it looks pretty clear that it was likely the 3rd explanation. IMO, he compounded the issue by trying to rationalize his comment. He would have been better off just saying something like, "Oh, wow. What I said was way off base. I wasn't thinking. You are right. Hitler, and the Nazi's, did use chemical weapons. I don't know what I was thinking.".
The guy screwed up. Normally, I would say that he should be allowed to make a misstep. But, it is not like he didn't have a chance to think before he made that statement. No one caught him off guard with a line of questioning that he wasn't expecting. He came out on that stage, planning to say what he said. The simple fact that he didn't run his bullet points by someone else before speaking to the nation, makes it seem like he is not doing the job he was tapped to do. This was a completely avoidable mistake, and it makes him look like a guy who is not trying hard enough to live up to the minimum standards of the job he is being paid for. IMO, it is completely justified to call him out on it. My bet is that, if he continues as WHPC, he will be more diligent, with his preparation, going forward.
It is not asking too much for him to hand his speech (or a list of bullet points) to a co-worker and say, "look this over...is there anything I should take out, or anything that I am forgetting?".