I see people talking about SEO and Dolphin over in the Boonex Unity forums from time to time, but not that often. When they do it's almost always the very basics. Some of which isn't even relevant or used anymore.
What I see discussed are things like the site title, meta description, and meta keywords that you can add in your Dolphin Administration panel. Meta keywords will not help anymore. All three major search engines have stated publicly that they ignore meta keywords completely. So I wouldn't spend too much time worrying about them.
Your site title is important, but meta descriptions are more about displaying a specific snippet of information/description in the search results. If you omit the description most search engines will display a snippet of text they find relevant to what you are searching for instead. So if you want something specific meta descriptions are helpful for this.
SEO can be difficult with Dolphin because if your site is private, requires membership, and that kind of thing to see a page that means Google can't see it. So if you have pages and content that someone needs to be logged in to see, then you can do all the SEO optimization in the world on the page or post and it's not going to help.
There are two kinds of SEO. Onsite and offsite. Onsite obviously involves things that you do to pages/posts, titles, on page/in post keywords, adding a sitemap, h1/h2/h3 tags, image alt tags, and those kinds of things. Providing they are publicly accessible to search engines.
Offsite SEO I rarely see talked about with Boonex Dolphin. I don't know if most people are just not that familiar with it, or if they are still living in the mid 1990s when onsite SEO was a bigger factor.
In today's world offsite SEO is just as important, and probably more important than onsite. You really should be doing both.
Onsite Dolphin SEO helps tell search engines what your site and content is about. Offsite SEO will help you rank better in the actual search results. So if you are only doing onsite optimization then you are saying hey Google this is what my site is about. Google says OK thanks, but nobody cares about your site.
Why does Google think nobody cares about your site? Because you are not doing any offsite SEO, or not enough of it. If nobody is talking about or linking to your website, then Google doesn't think it is important enough to return a decent search result for it. Google goes we found other sites that are more popular, being talked about, and that others are linking to so we will show these ones first.
So the bottom line is you really should be working on at least some offsite SEO. You don't want to overdue it or engage in activity that is of poor quality. You can harm your site more than help it if you are not careful.
Google is constantly releasing new algorithm and penalty updates. It is important to be aware of them, and to make sure you follow the guidelines and rules. There will always be people that cheat the system. Sometimes they get away with if for a while, but you can always tell by someones anger when it catches up to them.