Yes it is possible but involves a bit of explaining. In this case you should use standard routing mode. You have to route the outputs of the UnitY engines to the physical outputs of the UnitY I/O.
The engines can both be routed to OUT 5.6 and/or OUT 7.8 (if routed to the same output the engines will be mixed according to the settings of the engine faders). Thus, if the Engine output is set to OUT 5.6 or OUT 7.8 this engines output will appear on the digital output of the UnitY card.
The signals sent from DIGITAL I/O page 3/5 which normally would appear on the digital ouput of the card, will be replaced by the engine(s) output.
The idea of routing the engines to the digital output and then externally back into the 02R is possible. BUT, with an ADAT/TDIF output you have either ADAT OR TDIF out. None of them can be routed directly back into the 02R itself.
The 02R have AES/EBU and S/PDIF inputs (2TR In DIGITAL #1, #2 & #3) but you cannot connect to them without having an external box converting the ADAT or TDIF signal from the UnitY output to S/PDIF or AES/EBU.
Please note that the connector for TDIF uses the same 25 pin D-sub connector as the AES/EBU I/O but the format is completely different - and - cannot be used to interface to S/PDIF.