I have been thinking about your concern that your road agent may have a "conflict of interest" if he is allowed to hire and coordinate road maintenance contractors while also "hiring" himself to be one of the maintenance providers.
I do see this as a potential problem. Your agent's choice of maintenance providers could be influenced by their willingness to use him and his truck in the project at hand. This "conflict" could be deemed acceptable to the board based on availability of local contractors and the value and necessity of the service provided by your agent.
In our road association, with advice from the board, the President/Road Commissioner, who has no direct financial interest in road maintenance services, acts as our "road agent". I hope this helps.