Well, apparently there's one you can summon with a specific dragon shout, so I'd guess he's a pretty cool guy.
The question is, does the dragon in question really obey you out of benevolence? From reading about the shout, I got the impression this was more along the lines of gaining domination over the dragon, which might mean that it has no choice in the matter, and would still gladly kill you if it were possible to do so.
But as to whether we'll encounter dragons on your side, other than ones summoned by said shout, the answer is we don't know. While they are intelligent, that doesn't mean they'll want to help you, most Dremora in Oblivion attacked you on sight too, even though they were intelligent and could speak, and while there were a number of Sixth House members in Morrowind who could speak to, none of them were actually on your side. It comes down to a question of whether any of them have a reason to want to help you, or at least not want to help Alduin and the rest of their kin, so, will that happen? I don't know, it has a lot to do with how the story unfolds. really. I don't doubt that most dragons we'll encounter will be on our side, but would there be one or two exceptions? The only answer I can give is "maybe".