Its never stated that Gen-3's have a brain AFAIK. However, even if they did, it too is synthetic. A CPU made to look like a human brain. As I said, organic brains can't receive software updates to their OS.
Except for the part where they
1. Don't sleep.
2. Don't need to eat.
3. Don't need to drink.
4. Don't need to worry about radiation.
5. Can't reproduce with humans, for obvious reasons.
6. Have all of their DNA, and 'organic' material be synthetic. Even their blood is stated to be synthetic.
Then yes, they look like humans.