IP. Nexus appears more for companies and business boards. It sounds like a CMS. Are there any uses for it outside of such boards?

Can it be used as a blog like Wordpress?

Would there be a way to convert a WP database over to it somehow?

Would I be able to set it as the main page/area?

Technically, yes, you can use it as a blog. If you skinned the 'articles' system to a blog theme, it would work quite well

For example, IPS Resources (resources.invisionpower.com) uses IP.Nexus to power all of the website

Do you think there would a way to import Wordpress entries to it? Or would that require someone to make a tool or having it manually done?

When I was making a full site using nexus, I saw a option to import RSS Feeds ... So it might be possible if Nexus becomes live again...lol

Yeah Nexus supports it, we use lots of different RSS feeds at IPSR, in any community project page, the 'bug list' is simply the article system importing from the Tracker RSS