Only if it's common knowledge that both players are human.
ETA: Since I got downvoted, maybe I wasn't being clear. I think that the Warren Buffett quote applies to human psychology more than to game theory in general. If outright deception were easy, it would probably become a good strategy to keep your allies in some doubt about your intentions, as a bargaining chip. But we humans don't seem to be good at pulling that off, and so ambivalence is a strong signal of opposition.
Now that you have clarified, I wish I could downvote a second time.
Tit-for-tat is a good strategy in the iterated prisoner's dilemma regardless of whether the players are human and regardless of whether the other player is "on your side". In fact, it is pretty much taken for granted that there are no sides in the PD. Dre was downvoted by me for a complete misunderstanding of how Tit-for-tat relates to "sides". You were downvoted for continuing the confusion.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).