EA Canada are developing two sports games for EA Sport this year, NHL 12 and FIFA 12, where both feature physics, so I'd safe to assume it's in-house. And don't pay too much attention to the names as each game has it's own name for the technology. For instance, physics will be called "Impact Engine" in FIFA 12, while NHL 12 calls it "Full Contact Physics Engine". Or what FIFA calls "RailTracks", Madden and NCAA calls "Locomotion" but in reality it's the same thing.
All in-house games share as much technology as possible to reduce costs. EA's Crysis 2 and the upcoming Battlefield 3 uses ANT (ANimation Toolkit), which previously was only used in games by EA Sports.
But I agree that the Impact engine appears to produce more natural looking tackles compared to most of the usage of Euphoria. Euphoria does a lot of things right, but some of the stuff it produces looks like it's going in slow-motion - I'm thinking of Backbreaker's moon-gravity tackles or, say, falling of a bike in GTA IV.