Yes, people are using in production. Last community meeting we had some folks reported a large server deployment in the UK (in the order of thousands of servers) that was being partly transitioned to snaps. I think that's the biggest use I've personally heard about so far.
There are some people interested in having them working on 14.04, btw. It'd be great to see that working well.
I'm still on 14.04 and would be interested to know what the most popular uses for Snaps might be.