Yes, the same system is used in mainland China.

Apart from 4 and 5, you can kind of see the link between the written form of the number and the hand signal: 1, 2, 3: obvious because 一二三 6: the thumb and pinky make up the bottom part of the character 六 7: If you look at your own right hand upside-down when making the gesture, the bird's head points in the same direction as the 七 8: Your thumb and index finger are the two lines in 八 9: Your index finger is the second stroke in 九

I don't know whether this is coincidental, or even just my imagination...