Yes, this works, but you will inevitably get dropouts at some point. When using two different sound cards, both will have their own hardware clocks (quartz crystal oscillators) and even when you set them to the same sampling rate they will inevitable drift apart and then cause dropouts. The only way to solve this is adaptive resampling. Adding another input to your jack system via zita-a2j will take care of this issue through the zita-resampler and also will allow jack and Pd to run on a higher sample rate (an added benefit!). A well tuned system with a good sound card should be able to run 48 kHz with a block size of 64 samples (or better). Higher sampling rates and lower block sizes will reduce latency, giving you an improved playing experience and the feeling of intimate control.