If you have users that were created in AD but not through the SBS console, you'll notice they will not be present in the SBS console. This can be a nuisance for management purposes when you're used to using the SBS console for administering users, but it can also become a problem for some SBS functionality, such as the SBS POP3 Connector. There is a way for your users to be added to the SBS console without having to recreate them, though.
When querying the list of users, the SBS console in fact looks for a certain AD attribute inside each user. This attribute, when set, will enable listing in the SBS console. So, by setting the attribute, you will in fact "import" the user in your SBS console, allowing administration and enabling SBS functions.
From here on, your users will be available in the SBS console. Although you could further change attributes from within ADSI Edit, it's much easier to do the rest (e.g. allow access to RWW/OWA, assign user roles, ...) from inside the SBS console.