I actually hadnt figured out the "annihilation"-connection, I was just like "oh, a guy whose name comes from the word nihilism, very original" and that was it. I never liked the character enough to start thinking about the name.
And if someone hasnt figured out,
Vader=Invader
Sidious=Insidious(this should be pretty clear for any of us users here )
My point is, all the sith lords have names that are poorly "camouflaged" words depicting them, so there is nothing extragavant about Nihilus.