Linking Blog and website sitemaps

I am setting up a website with a WordPress blog incorporated. I have a WordPress sitemap generator plug-in, so I have a sitemap for the blog section. I have also used an online sitemap generator for the rest of the website, but it doesn’t index the blog pages or posts.

I imagine this is a common arrangement. Does anyone have an idea about whether it is desirable to somehow incorporate the WordPress sitemap into the main site sitemap, or is it better to have two separate sitemaps?

Thanks.