In your domain registrar, you can add as many sub-domains as you want.
But in Blogger, each Blog (ie combination of Posts and Pages) can only be pointed to one URL (ie to either example.com OR contact.example.com)
What you could do it set up a 2nd blog, which has exactly the same design as the first one, and set its "home page" to the contents-page content. (Don't give it any other posts.) Then redirect this 2nd blog to contact.example.com.
- You now have two blogs to keep "in synch" if you ever do design
changes in future.
- The home-page redirect option doesn't work for mobile viewes if you
have a mobile template enabled. (so it may or may not be an issue
So if you're doing this just for the "SEO benefits", I'm not sure that it would be worth the effort.