Cyanogen Mod support official for Nexus 9 live on their download page
CM 12 is Lollipop which means that not that much will change and you will not have to give up many features. This first official build is a nightly, which means you will get lots of updates and you should expect for bugs.
CyanogenMod will need you to have an unlocked bootloader and custom recovery, but Nexus devices pose no problems in this aspect. If something goes down bad, you can flash a full system image to fix it!