You can use the below API to get the site servers.
Altiris.Common.Collections.Generic.ISet<Guid> _installedServiceGuids = Altiris.NS.StandardItems.SiteServer.SiteServicesManager.GetInstalledServiceGuids();
Altiris.NS.StandardItems.SiteServer.SiteServiceController[] _installedService = Altiris.NS.StandardItems.SiteServer.SiteServicesManager.GetInstalledServices();
Regards,
Ashutosh T