I've just configured WSUS statistics, and most of the channels appear to be correct. However, the channel 'Computers up to date' show a value of 0, while my WSUS console shows that 18 computers 'need 0 updates' and have a green check mark next to them.
I also do use WSUS Package Publisher to make other software updates available via WSUS. The Windows Update client on my computer shows that I have no important updates available, and four optional updates available. The optional updates are managed by WSUS PP.
WSUS and PRTG are running on the same Windows Server 2012 r2 machine.