Rather than find broken clients, I would ensure that all clients are healthy. What does Altiris health mean in your environment? Is it patch compliance? Is it reporting a weekly inventory? Is it checking in with the NS within the past 14 days to report event data or receive a configuration update? Based on these criteria, create an exception report which lists agents in your environment that do not meet these requirements.
Combine this exception report method with a discovery that ensures all computers in your environment have an agent installed.
Your procedurement and retirement procedures and processes will also impact agent health. You want to ensure that when you receive a new computer, the workers responsible for receiving the computer understand the process for installing the agent. Likewise, you want to ensure that a process exists for identifying retired or disposed assets and deleting the agent from the CMDB or otherwise retiring the agent.
By ensuring agent health at beginning and end, and using exception reports in between during the maintenance phase, you can ensure that Altiris is functioning properly on all endpoints in your environment.