Unfortunately using OPMONis and the delivered Software from APC is not possible simultaneous. The APC software is blocking WMI, which makes your UPS invisible as batterie for windows. You can easily replace the original driver by following some steps explained in the pdf provided by Schneider Electric. This should make it possible for OPMONis to locate the UPS in your system.
Probably now the APC software will complain that it cannot find the UPS, but this will not effect your system or your UPS security in any way.
Even with running systems it is possible to switch drivers, so you can use your maintenance software provided by APC is possible at need.