sidebar widget itself works as a sitemap and i havn't seen any issue with google indexing inner pages. just make sure googlebot visits your site oftena dn all of your internal pages will be crawled. but you can do a sitemap if you want to, no harm doing that
I would recommend doing a sitemap just to be sure - it can't hurt, and it requires no effort on your part, because there are WP plugins that do it for you. The one i use is Google XML sitemaps by Arne Brachhold. Here's the homepage for it: http://www.arnebrachhold.de/redir/sitemap-home/ Good luck!