ARM = Gonna get boned
I use ARM's only on quick flip , new construction to keep my payment outlay down while the houses are on the market, once sold I simply pay off the entire ARM to convey clear title to the new owner, I would never recommend a ARM to anyone that I liked for a normal purchase,
As to your friends lack of abilty to verify income, boy that makes it tough , short of a spousal unit with good income (valid) he will be hard pressed to go it alone , hence the need for a co-signer, unless of course the loan can be secured in some other way , like another piece of property that is paid off .
Todd