I do not think so Legally you must defend a trademarked name or you risk loosing your trade mark. I have seen sites shut down that contained the original url in the title e.g:
neopetsgamehacks.com
Would be extremly easy to shut down. But I am not sure about domains that only sound alike.
It is also a forum basically about neopets so probably not. They wouldn't even be able to argue that it is so close that people may mistakenly think they are the same thing. If it were another game site like neopets than maybe they would have a case but since it's a neo related forum for players to talk i doubt it.
I didn't really look into it all that much but it seems like they are focused on modifying neopets, which should be fine. I think on youtube they call it a creative commons license which allows people to put up copyrighted music as long as they change the video or something small like that.
Leopets has been around for several years, it's non profit and it clearly states it's a neopets fansite, why would neopets care enough to make it disappear?