No doubt there is some military cracking/hacking from the US, but it is not needed. There is a well known public movement to hack Chinese sites and bring down the great firewall.
Hacking the Chinese military publicity site serves very little, if any military or intelligence purpose. It is also not great timing with Obama, etc.
Defacing a site is not the realm of state funded hackers/crackers, what they want to do is covertly infiltrate and obtain information, which isn't available on public sites anyway.
The Chinese state hackers ate targeting military, civil service and scientific closed networks.