The short answer is that anything that you could poll from an operating system normally is available to the agent. In fact, installing the agent is usually advantageous not limiting. For example: a node with the Agent tends to use less bandwidth when communicating with Orion. An Agent is required if you want to use a node as a Probe in Netpath. However, the agent isn't required for general polling if you would prefer to do SNMP or WMI natively.
Here's some information you may want for your detailed review:
This link has an extensive list of articles about the agents under its own category:
Specifically this article will give you some information about polling with Agents in general:
This article specifically talks about using less bandwidth than WMI:
Thanks .. !!
Can we get parameters list supported for both these monitoring i.e. agent less and agent based ??