I looked at dbo.inv_client_task_resources and dbo.inv_aex_ac_client_connectivity tables. The client task resources table seems to be most accurate in reporting the state of the agent. It reports the agent state relative to the task server it is connected to. if the task agent is installed and in a state to receive tasks, then the system is considered "active" or online.
If anyone finds a better method please share, otherwise I am going with this as a solution.
For anyone on 7.1 SP2 and needing to get a list of active/online computers, you can use this query.
SELECT Distinct
[db_name].[dbo].[vcomputer].[Guid]
,[db_name].[dbo].[vcomputer].[Name]
,[db_name].[dbo].[vComputer].[IP Address]
FROM [db_name].[dbo].[vcomputer]
INNER JOIN [db_name].[dbo].[Inv_Client_Task_Resources]
ON [db_name].[dbo].[vcomputer].[Guid] = [db_name].[dbo].[Inv_Client_Task_Resources].[_ResourceGuid]
WHERE [db_name].[dbo].[Inv_Client_Task_Resources].[IsActive] <> 0
;