In some ways but not others, according to this post by Catsy at The Brothers Brick:
- It was near-impossible to pull the legs off–I sawed through them where they join above the knees.
- The tab that connects the waist to the torso is completely incompatible with any standard System connection I’ve tried.
- The hands are not angled forward the way a minifig’s are–so accessories with a pronounced rake to them may not look as expected.
- The lack of wrist articulation is extremely limiting in terms of how you can pose them with accessories.
- The stud connection point on the feet is in the front, under the doll’s center of gravity and more or less directly under the body. The feet are slightly oblong.
- The legs have a very slight backward sweep on the way down, which you can see most clearly on the right leg above. The upshot of this is that it is impossible for a mini-doll to stand on any 1×2 area that has anything immediately behind them.
- The neck is a standard 3mm bar connection rather than stud-width like a minifig neck–the heads are incompatible with minifig torsos.
- The head is approximately the same dimensions at the top as a minifig head, but tapers towards the chin in a roughly egg-like way.
- The nose causes complications with some fully-enclosed headwear, but not most. The chin extends lower than a minifig’s chin, so that headwear with “chin straps” obscures the mouth.
- The hair is interchangeable with minifigs–and many TLC minifig hairpieces look quite good on the girls... it is made out of the same kind of soft plastic as the Exo-Force hair, and has tiny holes on the top and side of the hairpiece that go all the way through, allowing the attachment of hair accessories.
- Brickarms helmets work extremely well and look great. I do NOT recommend trying to use aftermarket hairpieces, however–I tried putting a third-party hairpiece on one of them and had to use pliers to get the head back out.
Note also that the legs do not move independently of each other - both left and right legs are on the same hinge. Not really a compatibility issue, but it greatly restricts the poses available without modification.
From the official press pack:
