Combining two databases

i’m not sure what the wp multisite offering can do or not do.

my site has a domain and subdomain structure. the domain and sub have their own database. the layouts for each a bit different. it was built in 2007 before wp provided multi-layout features. the visitor has no idea the site is built this way. however if they want to search for something it would be nice if one search menu searched both databases, etc. will the current wp multisite offerings allow me to combine this or that.