It is possible to use the input and output of the same sound card separately from two programs as if they were on two separate sound cards, at least it definitely is on Linux and the versions of Windows I tried. The sample rate and resolution do not need to be the same, either. Using the same sound card for both playback and recording also has the advantage of no synchronization issues due to a slight mismatch in the clock frequency of the ADC and DAC. But you need to watch out for grounding issues that can make the results incorrect (this also applies to two sound cards in the same PC).
In this thread, there is some discussion of sound card based measurements that might be relevant.