Yes. You can import more than one demo on your site so you can use different pages and features from each demo.
However, you can only use one set of theme options on your site. So if you import your first demo, this will import the theme options from that demo, which includes all the site colours, logo and typography. If you import another demo, the theme options from this demo will be used instead for all pages.
Options like page, header and footer layout can be changed on individual pages so these settings can be set to what you want if a demo import changes them for your existing pages.