The VM from Ian Piumarta has sound support for OSS, NAS, SunOS, and Solaris.
Lex Spoon wrote a sound driver for Squeak 2.8, which used an mmap-based interface to /dev/dsp. By doing this, it was able to support the low-latency insertSamples primitive for inserting audio data directly into the kernel's audio buffer. Grab sqUnixSound-mmap.c if low-latency audio is important to you and you want to try and get it working with a more recent version of Squeak.