hmm, interesting question.
I would say that the difference would be like saying "even though I said ___," as opposed to "even though I said that it is ___"
ex:
クリスマスといっても、アメリカとは全然違います。
even though I said/say christmas, it's very different from America.
クリスマスだといっても、予定はありません。
even though I said it's christmas, I have no plans.