Google.com search for
"is non-profit": about 90,000
"is nonprofit": about 41.200
"is a nonprofit": about 1,930,000
"is a non-profit": about 1,660,000
Of course, this doesn't take into account the context.
Perhaps "Wikipedia is a nonprofit organization" (or "non-profit
organization") if you prefer. Of course, that exposes the
"organisation/organization" difference.