No, RallyPoint will only allow you to list one current military unit. If you have responsibilities to multiple units, you should choose your primary unit (probably whichever writes your annual performance report), and then in the experience description add details of any additional duties.
We realize that many people have multiple roles sometimes, especially in the National Guard and Reserves, but we do this to keep the system as streamlined as possible, and to avoid confusion on where exactly is one's primary place of duty.
All policies regarding your RallyPoint Profile can be found in RP 3-1
Feel free to write us with feedback anytime.