A lot of pro equipment has the option of using the S/PDIF stream for clocking to maintain synchronization across multiple devices (e.g. recorders). But most will buffer it, or have the option to buffer it, to clean it up a bit especially if synchronization is not critical. For consumer systems, with almost zero research, again some do and some don't. Most all are asynchronous on the USB side and generate their own clock, but it is not clear to me after a ten-second look at some spec sheets what they do on the S/PDIF side. Several years ago I looked at the datasheet for a S/PDIF chip that included internal CDR (clock and data recovery) that pretty well isolated the DAC inside from the external bit stream but I have no idea if they all do that.
In any event, clocks are generally pretty clean, and you are unlikely to hear audible degradation unless it (jitter or clock wander) is really bad.
Which is a long way of saying "I don't know", sorry... - Don