TIM is not a Reaper agent yet.
The potential does exists for any character in the series to eventually become indoctrinated by the Reapers and become an agent for them. However, there are certain characters who's traits don't lend them to being indoctrinated for both story purposes and because they know too much and are not inclined to allow it to happen. TIM is one of these people. He almost exclusively works through proxies, and the closest he's likely to be in contact with Reaper tech in any significant duration is through a Quantum Entanglement communication device (several clusters away, in other words).
Those major characters who have fallen to indoctrination all did so before they knew its nature of what they were dealing with, notably Saren and Benezia.
TIM may take risks with his Cerberus teams and facilities, but he has too much value to the organization to place himself around such hazards, and his innate paranoia will protect him from the potential of being indoctrinated.