If you do not use the SBS provided ways to add new users they will not show in the SBS Console > Users and Groups > Users tab, because the user’s Active Directory (AD) attribute msSBSCreationState value is not “stamped” to Created.
Here is a quick review of the two SBS provided ways adding user accounts from the SBS Console:
Add a new user account wizard , and Add multiple user accounts wizard
Only these two wizards are recommended to add new users to assure full functionality for each user in the SBS domain. For example, to add a new user, start the Add a new user account wizard and provide user account information including user role:
Provide a password fulfilling the password requirements and click Add user account — Wait until the wizard completed adding the new user account to the network — If required, add or assign an existing computer to the user and then click Finish to complete the wizard