Hi Joshua
In my opinion, yes the blog should be consistent with the theme of both the website and the brand. Users can get thrown off by different visual cues and it can create a less than ideal user experience. While the blog isn't going to be sales driven, it's important you give user's a consistent user experience. That's how brands are built and how your audience will remember you. Keep in mind - this will be the first time some of your audience will access and interact with your brand. First impressions are the most important.
Hope this helps! Good luck!