When the label "pays" it is the artist that is paying.
The label bills the artist. I have heard artists complain about award shows and how they pay for it and dont get sales after.
Now if you are an artist with a positive outlook you know all publicity is good publicity and you could do a show or 2 and recoup.
To an extent. It can be negotiated as to where the money comes from. Depending on the size of the artist they could be on the hook for half or nothing. If they have a branding partner or 5 then, they pay nothing. There are people that work at the label's whose whole job is to get those partnerships for all these events. But like I said that's on the music side. As far as artists complaining about paying for the show and not getting a sales bump, possibly, but then their project was probably already in trouble because a label generally won't pay to lose.