Last I heard, Whisperpush on CyanogenMod only actually worked if you had the GApps package installed which isn't entirely legal and certainly isn't something they could get away with including as standard.
The best disclaimer sentence I've found here is: The Google Apps packages are NOT SUPPORTED in any way by Cyanogenmod. Not exactly a huge endorsement, but saying it's not entirely legal is something else entirely.
It depends. If you are installing CyanogenMod on your phone, then installing GApps is not very legal. However, Cyanogen team has been working with Google to get devices like the OnePlus One certified by Google and preloading them with fully legal GApps package.
