Yes, Uninstall command lines for Symantec Management Agent uninstallation works for 7.5 & 8.x versions, even if they don't have connection with Notification Server.
Examples of available uninstall cmd lines (In case of enabled UAC on client PC, open cmd as Administrator):
C:\>"Program Files\Altiris\Altiris Agent\AeXAgentUtil.exe" /clean
C:\>"Program Files\Altiris\Altiris Agent\AeXAgentUtil.exe" /uninstall
C:\>"Program Files\Altiris\Altiris Agent\AeXNSAgent.exe" /uninstall
And If you had checked "Add/Remove Program List" checkbox in Default Settings on "Agen Install" page, before Agent installation on client compouters, then you can uninstall Agent on required Workstations from "Add/Remove Program".
Thanks,
IP.