In the unofficial species menagerie listing, Defel get what on stealth checks in shadows?

Also does being sil 0 give you a bonus to stealth?

Check the core book pg 392 for Defel Bonuses and Setbacks (in the entry for Defel Assassin). Also note that officially Defel aren't listed as Sil 0, just sayin.

And no, Sil 0 doesn't have any built-in formal bonuses to stealth.

Defel are not Sil 0, there is one in the Jewel of Yavin adventure as well if you want more references.

Do check out fan-made adventure called Cold Comfort from Shadow of the Broker series. It uses Defels in all their elusive beauty.