The OnGrid Tool does not officially support single- or dual-axis tracking.
However, you can at least simulate production increases due to trackers via the Local Micro-Climate Adjustment Factor (under the Solar System & Site Variables Section). This factor is simply a production multiplier. So if you anticipate a dual-axis tracker will add 20% production, for example, you can enter in 120% in that line.
Please note that this is a rough work-around; the analysis won't be very accurate with time- or seasonally-differentiated rate schedules.