...My dive instructor thinks hands down that snowmobiling is much more dangerous that even technical diving, let alone rec diving (which I find very surprising) so I wanted to get your thoughts too.
To make any comparison of value, one cannot only compare the statistics of others. The real question that must first be answered is 'How do you undertake these activities?'
I'd suggest that one of the least dangerous things to do is to sit at home on the coach. One of the most dangerous things might be sitting in the middle of a high-speed highway on the coach. It's not the activity, but the location, attitude, training, etc. that a person has while doing it that presents the danger.
Clearly both activities can be dangerous (Divers and snowmobilers die every year). Statistics mean little to those that do and people don't die that statistically may have a higher risk. Whatever you do, do it within your safety envelope. There are never any guarantees...