Supposedly he was the one responsible for getting the 1992 dream team in the game too, even calling a couple members of the team to get them to agree to be in the game. I guess it's fine if he wants to do that, but I do find it odd that they had to put that on the front cover. It gets worse than that though. Justin Bieber is a playable character in the game.
I seem to recall being more excited that Snoop Dogg made an original song for Need for Speed: Underground 2 last generation. Maybe because that's because I enjoy racing games more than I do basketball games.
The NBA2K games are generally some of the best reviewed, AAA sports games released every year.
Secondly Jay Z producing a basketball game isn't really a stretch. He has a shitload of money and is the part owner of an NBA team. Bravely Default? That doesn't even make sense.
Thirdly this type of business is why he is one of the wealthiest celebrities on earth, regardless of how you feel about his music he is one hell of a good businessman.
Fourthly if you think the producers of most major games are "doing all the work" in the making of it, I think you need to look up what producers usually do. They oversee projects in a broad sense. I'm sure he gave some input, not unlike all of these movies that Tarantino supposedly co-produced when in reality he filmed like half of one scene and gave some pointers, said what he liked and didn't like and financially was vested in the project somehow.
In short I see no problem with this. It makes about as much sense as him selling vodka or owning exclusive clubs.