Can I format an SSD as one of the read-only CDFS-style formats?
Yes. You can use mkisofs to write directly to your SSD, no existing filesystem or partition table necessary.
mkisofs -o /dev/sdg /path2musicdir
Then the block device (SSD) can be mounted the same as any other iso file
mount -o loop,ro /dev/sdg /mountpt
NOTE: Files need to be named in an 8.3 format, unless you use the Rock Ridge, Joliet, or HFS/Unix extensions, which presumably will take a few additional bytes (a few fewerfewer files for the sake of intelligent file names.)