Not risky. Your current spec is the main concern, and you said it was good for 20ma, right? You confident on that current spec? It's enough to light an indicator LED.
Yes, the output high level voltage will probably be a couple two or three tenths of a volt shy of the rail, but so what? That just decreases the current, if you figure the resistor based on the supply V - led forward drop V. 47Ω puts you below the danger zone off a 3.3V supply.
GPIO is general purpose I/O, equivalent of a parallel port. It's there to run things like this.