I have licensed and put out a couple of tracks in my time, mostly on vinyl. But in most cases, in my experience anyway, the rights are not owned by the artists themselves. So they get little if any of the fees paid. If they wrote the song then they may get some part of the mechanical royalties paid to MCPS etc.
In the case of compilation CD's the amount paid per track (usually a small advance plus a percentage of the dealer price divided by the number of tracks on the CD) is likely to be not much at all.
But even so, to echo what Ady says. The artists are generally very happy to receive the recognition that they get from a legitimate release of their work.