Hi @jayh,
Any website development project should contain some element of SEO, and most agencies will take this into account when designing and building a new website. For a GDD project, SEO factors should be constantly tested and iterated to ensure that the website is performing as effectively as possible.
This mostly takes the form of technical SEO, testing page load speeds, ensuring the site map is correct etc. However, it’s likely that there will be a fair amount of on-page SEO too. GDD is all about improvement over time and, as the goal post are constantly changing with how search engines determine rank, I’d say that an SEO strategy is an important part of your offering.