How do I effectively have multiple helpdeskers use ARD?
It sounds like you need a client management solution.  I prefer the Casper Suite, but in the interest of full disclosure, I work for the manufacturer.  However, I was a customer for some time before becoming an employee.  There are competing products and I advise you to evaluate more than one solution before making a purchase.

With all that said, a client management solution will give you a central inventory system, and centralized management tools.  The information regarding your inventory and management tasks are stored on a server that is accessible to your entire staff, and depending on the privileges you assign, all members of the team can perform management tasks.

I hope this is helpful.