Yes, but you'll need to do the mknod yourself, and have a program running in userspace reading from the block special file (or fifo).

I've used portaudio from Python on OS X before for doing this kind of audio manipulation.

/dev/audio doesn't exist. i think sounds go through core audio or something. i'm not really sure.

the command say is pretty interesting though

As far as I can tell, just by loading up Linux in a VM, but of course, that's cheating :)