Multi-DB with Buddypress, Marketpress & WPMU

We have Wordpress MU installed with BuddyPress and the WPMU Dev e-commerce plugin, Marketpress.

The functionality we have working at the moment is exactly what we needed.

One site/customer adds a product to Marketpress. This product is then seen on the global product list on our main Buddypress community site.

My question is does Multi-DB break this functionality. I'm a little confused as to how exactly Multi-DB works. Does Marketpress scan all the available databases for products to build the global product list?