Hmm... I've never heard of Nihlus, and upon looking it up, the only thing I could find was that it's the name of some monster-spectre thing haha... (if you're not familiar with what I'm talking about, look it up on Google ).
To be honest, I think that a lot of people would mispronounce and/or misspell Nihlus, and those aware of the spectre character thing may associate it with that. I had to keep checking your original post to make sure I was spelling it right! It seems a bit too unusual to work as a boy's name for me, unfortunately.
That being said, I like the sound of Nihlus and understand the appeal. I love the 'Ny' sound in boys names... how do you like Nile/Niall, Niles, or Nigel? I think those are all slightly less unusual choices that would fit a boy nicely.
If you really love it, though, then I think it's a cool-sounding name. Hope this helps!