I’ve seen it go both ways, and have accepted commissions both with and without drawn references? I’m of the opinion that either a reference or description works fine. Of course, with either a visual reference or a written description, the more detail, the better : ) If you’re not sure, then just provide as much info as you can/feel is necessary~
I know some artists do have their preferences in regards to this, though, so if you can find what that is, better to comply with it. : )