The simple answer is no – search engine submission isn’t necessary. The majority of search engines nowadays (most notably Google) crawl and index pages by following links. Using that logic, a single inbound link from any already-indexed page will identify your page to the engine. Subsequently, if that page links to other pages within your site, they will also be indexed… and so on.
For this reason, inbound linking is very important. In fact, acquiring back-links may be the most important of SEO. In theory though, a website owner shouldn’t have to ’scout’ or ‘hunt’ for links. If the presented content is of interest, useful, and/or important, there is a natural tendency among web users to link to information. This is the basis for the Google PageRank algorithm.