stephenh, NoMachine simulates the press of physical keys by sending the physical key codes. If you have the §± symbol on your keyboard, these are the symbols that it will be possible to input with NoMachine. How they are translated to specific symbols depends on the remote system.
Can you open a new topic about the issue you are encountering making sure to state the versions of NoMachine (client and server side) and the version of Red Hat as well, language set in desktop environment etc, and details about the Mac computer you are connecting from (OS version, keyboard type, language etc)