Wildcard SSL for subdomains?

I have a client who has 1500 subdomain sites. We're looking at a way to automatically have all the subdomains, plus any new ones added (they add a couple per week) covered by SSL. We're thinking of purchasing the Wildcard SSL through their cpanel so, essentially looking to cover everything under *.domain.com with this SSL. I assume that will work in that all existing domains will be covered with SSL. Two more questions: Some number of the subdomains have SSL assigned to them. How will the new Wildcard SSL affect them? I assume that all new subdomains added will automatically be covered. Is this the correct assumption?