Is there any difference between software metering on agent vs agentless?

Yes, there is some difference between agent and agentless data collection specific to software metering. Agent continuously monitor the software getting used by checking launch and termination of all the processes belonging to specific software. For agentless, we use different approach to collect this data, it takes live snapshot of running processes during metering schedule and arrive upon statistics. Hence while agents will not miss out any events between metering scheduling cycle, agentless may miss to collect details on certain software which are used between two subsequent schedules.