Is there an Option to group or categorize sites on MU

Hi,
I have a site recently installed...with Multisites..
Its a great tool
Only a question - is it possible to categorize Sites since i have multiple clients and also use ultimate branding in each of these Categories e.g. "Category A"= 250 sites -with login branding of Client A and "Category B"= 125 sites with login branding of Client B -

plus if I can create a user "Admin A" that i give access only to "category A" and "Admin B" to "Category B" I don't want to use another multisite installation...