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.
With all due respect, submitting your site to the search engines can’t hurt. Plus, it only entails about 5 minutes of added work assuming you only submit to the big guys. And once is enough… you don’t need to submit your site more than once. It doesn’t help or get your site crawled any quicker or more often.
It should be noted that submitting your site to Google, Yahoo, MSN, and many others doesn’t cost a fee. Many SEO companies assert that you need to pay to be indexed. This isn’t the case and I would stay away from these companies. They are money hungry and aren’t looking out for your best interest.