Well, they already have poor research, which I think reflects the generally low IQ and poor test results of the Ogre Kingdom as a whole
The air magic would reflect an inherant affinity, rather than skill or training. They'd just be predisposed towards air, occasionally, like Trolls are to earth.
And you'd still be paying 400 gold for the Slave Giant, it just would maybe make you stop and think a little bit more about them, if you got the occasional one with air magic.
I'd definitely give the Slave Giants a great big negative research bonus (who's going to use them for researching, anyway?), but it's an opportunity for the nation to have a different outlet for whatever the Ogres *do* research, so while it might not directly influence their researching a whole lot, it might give them more reason to bother.