I think they know who is Hitler, without maybe truly appreciating the scope of his murderous regime. There are plenty of references to nazism in Thailand, thur the TV/press, war movies, etc...
Maybe their college and University elders back then, but in 1992, Suchinda's mug was mainly drawn and painted on with hitler lookalike features. Fast forward: 14 years later (I was there in both cases), it was Thaksin's turn to be drawn as Hitler, and also likened to Hitler. I even heard people saying he was worse. Truly an indication they know little about nazism, but then again, there are plenty who also say, here in the USA, that Bush is worse than Hitler. So I believe that it is all very cartoonish and outlandish, but mustache-drawing thais would have no reason to do that if 1)they did not see some propaganda gain to liken a hated leader to Hitler 2) did assume that they are the only ones in thailand to know about Hitler.
To those who say that they have no idea really how offensive that can be, I am inclined to agree, yet, occurences of thais being offended, and raising hell and ambassador recall threat, etc.... when foreigners do stuff, at best innocent and at worse thoughtless , concerning thai monarchy, Buddha images and state of thai economy (far eastern econ review censoring a few years ago) should prevent us from being too indulgent. If they are not, why should we?