Mike, I can see two ways to do this: you can add a custom provider for your blogs that uses a connection string to the alternate site. this method is discussed in these posts:
Sharing Content Across Multiple Sites
Multiple providers for news, generic content
Alternatively you can use the RSS feed for the blogs. With this you can create a widget that reads this feed and displays the content on the other site.
The first option makes the external blog appear as if it is part of the site. In other words you would see both the list of blog posts and read them from the second site as if they were natively part of it.
The RSS option will allow you to just link to the external blog directly just like showing twitter links or something like that.
I hope this makes sense and is helpful! Let me know if I misunderstood your question or can be of any more help