I don't really think it matters either way. it's not a great song, but it's not a horrible song, so it's not disrespectful. i think jay-z set out to do a song based on (not really a cover or a tribute to Pac) "me and my girlfriend" and he did just that. that's it.
and, if you think about it, Pac had beef with Jay, but Jay didn't have beef with Pac, so it's not really an enemy being disrespectful or respectful to him; it's just another artist.