I think that whether or not you make a whistle for yourself or for profit... if you make a whistle with your own hands, materials you've collected, whatever design or concept you've come up with or are going off of, and your own desire to do so, then you're a whistle maker.
However, I think the common theme that comes to mind when someone sees the capitalized words "Whistle Maker" or even just "whistlemaker" is someone who has taken up making / tweaking whistles on a large or repetative scale and selling them to the public.
It's kind of like "whistlesmith" as some people choose to use. In my mind, that word brings to mind specifically those that make whistles to sell them. "smith"ing just sort of brings to mind blacksmith, gunsmith, etc. All those who make, remake, retool, refine, manufacture, repair, etc.
So... I'd say it's like most things on here... open to interpretation!
C-ME!
"Remember... No matter where you go... there you are..."
-Buckaroo Banzai