I am using Squirrel SQL against FMSA 11.
It works with older versions as well.
All I did was 1) registered JDBC driver 'fmjdbc.jar' and 2) created an alias for the FMSA.
Indeed Squirrel does work!
I gave up on it too soon when I couldn't work out how to register the driver. Knowing that it worked for you I gave it another shot and was successful.