From the RME driver download page you can already see that both interfaces use the same ASIO driver:
UFX+/UFX II, MADIface XT/Pro/USB, OctaMic XTC, ADI-2 Pro/AE/FS/DAC, Digiface USB/Dante: driver_madiface_win_09673.zip
From this you can deduce that the DAW can access both interfaces at the same time (as a DAW can work only with one ASIO driver at a time).
Since both interfaces offer synchonization via Word Clock, you can clock synchronize the interfaces, which is very important in such a multi-interface setup.
Additionally you need to take care, that both interfaces use the same ASIO buffersize, so that you do not get an offset by audio transmissions which use unequal buffer size (different amount of data being send in a certain time interval).
In terms of TotalMix FX you simply open a new instance, so that you have one TotalMix FX window for the one and another TM FX window for the other interface.
Of course you have restrictions, that you can not route audio across the two TotalMix instances.
In the RME driver settings dialog you can select for which of the 2 interfaces you need to produce WDM drivers, so that also Windows can make use this solution for recording or playing back audio (to be able to have a default windows sound device).
I am also using 2 UFX+ and one ADI-2 Pro with this one MADIface driver and my DAW (Cubase 9.5 Pro) has direct access to all 3 interfaces.
So from my perspective, even if my name is not Matthias, I would say, yes this is possible ;-)
Lets see whether my "crystal ball" worked properly
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13