SEP 11 to SEP 12 migration - Help needed

I have both SEP 11 and SEP 12 environments running independently of each other.  Both are running on Separate SQL databases.  We are working to decommission the SEP 11 environment. 

Can I simply upgrade my SEP 11 site to SEP 12 and point it to the SEP 12 DB?  Will this allow the SEP 11 client to communicate to the SEP 12 environment through the upgraded SEPMs?