Check out this page:
http://www.behindthename.com/top/search.php?terms=gabriel
Like a lot of Biblical names, it's particularly popular in the US.
It didn't appear in the top 100 lists for Ireland in 2002, 2003, or 2004 according to Behind the Name's data (see
http://www.behindthename.com/top/ )
Sorry, I have no idea if they use Gay as a nickname anywhere.
- chazda