Just been reading the Omex 710 manual and wiring diagrams ... A very comprehensive ECU which looks fully stand-alone to me ... Maybe it is not actually possible to disconnect it then as it is probably not classed as a piggy-back ECU in the normal sense.
If the OMEX is controlling everything to do with fuelling and timing and you have eliminated any compression issues and fixed the timig, then yes checking all enginer sensors for operation, correct installation and calibration and wiring would be a good move. The manual can be downloaded and shows all the pin-outs for each sensor so GDI could check to make sure the ECU is receiving the signals it requires
The OMEX also has data logging so GDI should be able to do some of that and check to make sure all the sensors are working correctly and are calibrated.
Martin
If the OMEX is controlling everything to do with fuelling and timing and you have eliminated any compression issues and fixed the timig, then yes checking all enginer sensors for operation, correct installation and calibration and wiring would be a good move. The manual can be downloaded and shows all the pin-outs for each sensor so GDI could check to make sure the ECU is receiving the signals it requires

Martin