Displaying Member Blog Posts By Post Category In Custom Loop On Main Site Home Page

I'm trying to figure out the best (most logical) approach to achieve the following on a WPMS install.

We need to display the most recent "X" number of Member Sites blog posts on a category by category basis in a custom query loop on the home page of the main site.

Our WPMS Setup Is Different Than A "Tradtional" Install -- As Follows:
1. All the Member Sites are setup by default with one theme.
2. All Member Sites use one common set of "global" Categories.
3. Members can't add or delete categories.

So we're working to "pull" the most recent posts from the entire network on a Category by Category basis. Let's say we have 4 "global" Categories for the network blogs -- e.g. "Dogs" "Cats" "Turtles" -- and these Categories are NOT used on the main blog and we want to show the most recent 10 posts for each network Category in their own loop on the home page of the main site.

I know the "Post Indexer" plugin will give me a table of all posts on the network but I don't believe it includes a "Category ID" in the table -- correct?

We haven't begun adding data to the network blogs, so we can change the Category structure -- and/or add Custom Post Types if needed -- no problem -- just need to understand a "best approach"

The answer I'm looking for is... "Here's how you do it with the Post Indexer" plugin"... or "Here are the plugins you'll need" or "This is a custom programming job and I'd generally suggest this approach in outline..."

I'm fine with contracting some custom work -- just need to get my head around an approach to the structure of the network blogs and/or how to extract the data to the main site.

Thanks,

Scott