Here's the diagram of a typical DeskAlerts Environment:
So to put in perspective of AD, Synchronization is nothing but a listing request that populates the Database. The request is made by default LDAP (port 389) or LDAPS (port 636). This requests pulls these fields form the AD - Username, password, E-mail, phone and after that, these users are now part of DeskAlerts organization independent of the actual AD.
After you have installed the DA clients on recipient machines, given they are built with AD, they will automatically pull this data and assign the user logged in as the recipient. However, they will not count towards DA license count until Synchronization was made of the OU this particular User is part of. Thus making it so Client will not receive any alerts and be visible unless he was synchronized. Once synchronized, the user will be part of DA Organization and will perform as expected.
If there are multiple accounts on the same machine, once user is logged out and another one is logged in, DA Client will automatically change the user.
Hope that answers your questions.