Joey's a bit of a jet dealer, and he will offer a piece of the New Reno experience for the low, low price of $500. A decent Barter skill can lower the price to $350, which is still 14 times what jet is actually worth later on.
Female characters can sleep with him, without much benefit.
Sleeping with him makes him move up on the map, closer to Becky's. As soon as the Chosen One leaves the map, he will disappear, preventing the Chosen One from getting Anna's locket unless he had been robbed of it. [verified]
The bug can be fixed by following thoses steps: Exit the West Side area of the Den and, while the game is still loaded, delete the file Fallout2/maps/DENBUS1.SAV. Then re-enter West Side and the map will reset – and Joey will be with the two other thugs.