Yeah, I see no problem with that method. The receiver DACs the signal and then is fed directly back to the soundcards analog input. As a benefit you have included and compensated for the receivers response in your soundcard file. Be sure you have no tone controls or soundfields on when you do it though.......
It's very easy to check the efficacy of your cal file by leaving the receiver in the loop after the calibration is done (and saved in REW) and do a measurement sweep with the new soundcard cal file loaded in REW. Obviously the result you're looking for would be a perfect flat line....
brucek