The “gray area” part is incorrect, because it’s not gray, and saying it’s gray encourages people to go ahead and do it, which perpetuates the notion that it’s gray.
Art. 43 of the Employment Service Act makes work illegal for foreigners. That’s the starting point. Instances of work being legal are merely exceptions to Art. 43.
Here’s an example.
If you want I can show you the decision. I’m sure there are similar ones out there.
By all means, find the gig first. But if you need to break the law just to get the gig? I know what my choice would be.