Yes, but only in the sense that it will threshold any input into a 1-bit signal. If you feed it audio you can use it as a primitive 1-bit sampler. You can even get something that you can play back as recognizable music that way. I haven't tried feeding audio straight in the read pin of the cassette port, but the C64 is so resilient that I'd be surprised if you wouldn't get reasonable results with some minor adjustments.
Still, you would need to cut it up or make an adapter of some sort, then connect that to the 3.5mm audio jack of some smartphone or modern computer. I can see how just copying to a tape may be less fuss.
Edit:
this adapter suggests it is a bit of hassle actually:
That adapter includes pointless leds and attempts to clean up the signal in various ways to make it more reliable. You can likely do without for a one off transfer, at the cost of some hassle getting your audio output right.
The 'simple stupid' approach is to cut off a 3.5mm cable, de-isolate one of the wires and tape it to the read pin. I've done that (just connected random analog signals straight to an io pin with tape) to interface to other ports on the c64. It's incredible what it will tolerate.
But sure, if you have both a cassette player and a datasette to hand, it will definitively be easier.
