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Yes, either way will work.
While the 600EX-RT has a new radio system, it also has a fully backward-compatable optical wireless system.
When set not to fire, the Master will still emit command-and-control flashes (and metering preflash when in ETTL mode), but not a flash for exposure.
The final command flash can sometimes be seen in reflective objects in the scene, or if very close to the subject, but there are workarounds for that, too.