I have a site with thousands of pages. The pages are dedicated to be found by the search engines as they are very specific. It is very unlikely that the users will find necessary pages using any navigation on the site. So for me, I'd leave the link to page only in the sitemap as it is easier.
But how would Google, Bing and others consider pages with no internal links pointing to them? Will they be ranked lower due to the lack of those links?