I found a theme sold via Envato called DocuHub, but I cannot find any means to ask them this question (Can Ghost be used to write blogs and technical books at the same time). This question is equivalent to asking whether Ghost can maintain two themes and dependent on the content type (blog or doc) switch theme on the fly.
A simple, but more expensive solution would be to run two instances of Ghost, each with its own theme
You can’t have two themes at the same time.
However with the Routes & Collections you can separate your content. For example having all blog posts on the index(/) page and having all doc posts under the /doc route.
There is an example in the official documentation how the filtering for collections is working.
Then you would probably need to add some new templates to the theme, to show the blog posts differently and maybe your homepage as well.