It could be still OK to use the addon, the reason for no updates could be that there hasn't been any need to update it - it just works. But just try it, you won't brake anything.
Mine does show ZoneLevels on the world map at the bottom, or at least it should. I have not really gotten a chance to to see, Since the new patch I've only been able to play a few hours here and there. You will have to check "Load out of date addons" in the addons menu for it to load.
Edit: You can also turn off everything else it does and hide it all.
As a current and long-time user of Cromulent, I can safely state that it doesn't throw out any errors and doesn't appear to have a single problem in the latest patch. The only potential issue would be making sure "loud out of date addons" is checked.