You want to make the TeamSite authoring interface WCAG-compliant, or you want to make your runtime website WCAG-compliant?
The former is virtually impossible. The latter has little to do with the platform, and everything to do with how you write your templates/components.
Yes TeamSite manages the content. Developers build what needs to be displayed and content authors fill the forms out.
So the developers need to create required fields and force the user to enter the complete information.