Ari -- I wouldnt use it, personally, I dont really like the name.
Ian -- I think it works as a nn, because some names that end in -ian, dont have any other nns so that works.
Reno -- I actually like it.
Axel -- certainly unique...but I think its a stretch as most people wouldnt guess what his name really was.
Silver -- I have considered this before, I really love it. I love the sound of
Silver (I do like the metal silver a lot, too, lol), and I think it provides a decent nn for the long
Sylvester.
Alis -- sounds like a girls name (
Alice) and, in fact, is the Welsh version of the name Alice...so no I dont like it.
Gene -- a stetch.
Genesis is pronounced like
Jen not Gene...so I dont think it works.