You can't outsource blogging
Sure you can hire (and lots of companies probably should) a "blog consultant" to teach you how to blog and how to use blog tools and help you figure out what you should be blogging but in the end the biggest thing about blogging is that it reflect the voice of your company, yourself and your organization.
No matter how "embedded" a PR person or a "blog consultant" is in your organization or how passionate they are about it, they can't really speak with the same voice as an internal person!
That's Web 2.0: people conversing on the Internet in their own voice about their passions and their organizations using Bryght sites and lots of other cool tools; not somebody else speaking for them.