They'd likely have really low interest rates [1] right now due to the federal reserve keeping the rates low, and presumably refinancing soon now that house prices have risen quite a bit (depending on your market, and loan details, of course).
The 6-month libor, which a few ARM's are pinned to is currently at 0.4%, in 2008 it was around 3%, so your ARM could potentially have a lower interest rate of around 2.6%.
If you didn't lose your job, and had a 3-5 year interest only ARM in 2008, it's possible you could have benefited from it (again, depending on your local housing market). This obviously didn't work out well for everyone, but ARM's are a risk that can pay off as well.
That being said, once rates start rising (possibly soon, according to the fed[2]), there could be another foreclosure bubble of people sitting on ARM's watching their rates climb up.
[1] http://www.erate.com/six_month_libor_index.6-months-libor.ht... [2] http://www.nytimes.com/2015/03/28/business/yellen-says-fed-w...