In versions of Bloo from 1.26 on, there is a setting in the Blog Profile for community blogs (sub blogs) that can suppress a Community blog from showing up in a front-page list of community blogs.

In the Blog Profile settings (Lists and Settings | Blog Profile) for Community blogs there is a check box near the bottom that is labeled "Allow this blog to appear in a list of community blogs on the front page of this community".

If that box is checked, if the top-level blog has a list of the community blogs shown on the front page, by having placed the _{BlooCommunityBlogs}_ tag in a front-page overlay, the community blog will appear in the list.

If the page is unchecked, it won't. This doesn't mean that no one can motor over to that blog from anywhere on the internet. It just means that that blog won't show up in the front-page listing.