The UnitY card acts basically as a ordinary Yamaha I/O card. However, the inputs for the two UnitY engines has to come from the 02R slot outputs ch. 5-8. Please refer to your 02R's Digital I/O page 3/5: Slot Output Select.
The selected Slot Output will naturally also be the one present on the digital output of the UnitY card. That is, IF you haven't chosen to route the output of the UnitY engine(s) to the digital output.The outputs of the UnitY engines can be either mixed with the digital inputs 5/6 or 7/8 of the UnitY card and will therefore appear on Mic 5/6 or 7/8 or you can mix the UnitY engine outputs and route them to i.e. mic 7/8 and mix the digital inputs 5/6+7/8 and route them to i.e. mic 5/6.
Beside the possibilities listed above we also have a feature called Ext. Routing: With the UnitY card in slot 3 or 4 you have the possibility to use the internal 8 analog inputs at the same time as you have access to the two UnitY engines. PLUS that you have, with a UnitY I/0 card, the 4 digital inputs (5/6 & 7/8) which can be routed to the St LR or ch. 21/22.
Please also check the UnitY manual. You can download it a PDF version here. See block schematics on page 17 and page 14.