Reading the documentation it says to enable SNMP, I assume on the Mac for Altiris to be able to discover it. Are there any particular configuration settings?
Here is what the CMS_MacAdmin_8_1_Guide says.
DiscoveringMaccomputers Network Discovery is basically the same for all platforms. The exception with Mac computersisthattodiscoverthemascomputerresources,youmustenableSNMP before running Network Discovery.