spare tire question

I've wanted to get a spare for my 2013 Volt. I have a source that has a Cadillac CTS aluminum spare. I have 17in tires and this spare is 16 in. Question 1. Can I use a 16in as a spare? 2. It's from a 2003 CTS and has a 35-40mm offset,70.3center bore, 5x115bolt pattern is this ok? I've seen the...