yes, with wp3 and newer style of wpmu and domain mapping plugin - you can preset some things in the theme by editing the theme on your main blog, the individual edits on each blog the the ATO will still work
For example on my main WPMU admin blog I have a corner peel ad - this is done with a javascript added to the header file in my theme folder for main blog - now this add appears on all blogs in my wpmu. I also have banner ad between each post, this is served using a javascript calling on openx and the script is hard coded into the footer area.
I realize this is a really old question - but with new wp3 and wpmu changes thought an updated answer was relevant