@Sven:
Several people have already addressed the matter since you posted this, but I feel it's common courtesy to respond to your post directly.
Quite true. Having re-read the chapter, it's clear that whatever attack Whitebeard was using, it was stopped with the Ice Ball. When Whitebeard stabs Aokiji, it's without any sort of enchantment. Probably why it did nothing. But, the scene now makes more sense to me. The reason that pirate chap was confused might be because he thought Whitebeard's weapon was still enchanted with Ambition.
Why would Whitebeared attempt to stab Aokiji without any type of enchantment? Surely being WB he would know hitting a Logia user with a normal attack would have practically no affect at all? The use of ambition obviously doesn't mean one person can automatically defeat someone who uses a DF, therefore there are obviously ways of combating ambition. Excluding the argument that there was a lack of glow when Whitebeared attacked there isn't much to say he didn't use ambition. I'd say it's more likely than not that he did.