Every company that makes a well functioning websites "does SEO". The easier white-hat practices of the past have come into common practice as part of what is considered good web development. Things like making sure all you navigational links are text, using consistent linking, and assigning correct alt tags to images go along these lines.

The the question that I think you might be trying to ask is "whether all startups go into the grey and black-hat areas of SEO". The obvious answer to this is no. Lots do though.