Found this in Antwerpen, and, being German, found it very amusing, too! Wonderful case of a "false friend"! https://bondagetop.files.wordpress.com/2014/05/7787637_5838cd3604_m.jpeg
I don't fully agree, in most cases they mean the same and could be used interchangeably. Arts doesn't mean GP in english, as, besided huisarts you also have tandarts or spoedarts for example.
There is one particular case in which you could not use arts, it is when addressing the doctor; so that would always have to be dokter. "Goedemorgen, dokter" for example.