Here is some helpful information on <a href=”http://www.novell.com/communities/node/3950/synching-multiple-address-books-lotus-notes-edirectory”>multiple address books.</a>
Yes it can support multiple directories, there are some limitations as to the type and data in the directories.
Are they just for viewing or email addresses? Domion support a Directory assistence db that lets you select the addtional directories and what they are sued for , email or/and access. It will also support LDAP directories.
If this is a customer directory there are some views that are needed such as ($Users) view that you can copy from a current Domino Directory and modify to fit your customer directory.
I do this for customer and web access directories all the time.