If you look at the fluff from 2nd edition Planescape, and the fluff from the 3rd edition Half-Fiend, then technically the half-fiend is the template to create both cambions and alu-fiends. The stats are wildly different from the 2nd edition versions, but they are both halfbreeds. In my opinion, the 3rd edition half-fiend (and half-celestial, for that matter) are closer to the 2nd edition version of the tiefling and aasimar, respectively.
I second the opinion to look at Green Ronin's Aasimar and Tiefling book... it's great.