[whpalmer4]

How much baling wire and chewing gum are you willing to tolerate?

You could build something similar to the scheme that OmniFocus uses to process mail into tasks. You would leave Mail running on some computer, and there would be a Mail rule that intercepted messages from your team members signaling that they had completed a task. The Mail rule would invoke an Applescript which would tell OmniPlan to mark that task complete.