There are tour guides inside the cruise terminal, they operate as tour guides but also as taxis, they are safe due to the certification received by the Mexican government and the regulations of the ship terminal administration.
check this website:
Acapulco Sun and Sand
The cliff divers are about 15 minutes by car and 35 minutes walking distance, but i will recommend to take a taxi. the cliff divers are located at la quebrada by the downtown, i wont say that is 100 % safe, but is not either so bad, it is just like any other city in USA, just follow the regular safety rules, do not talk to strangers, do not wear jewelry, keep your belongs close to you, and now you probably understand when i´m saying to hire a tour guide from inside the terminal.
Enjoy your trip and enjoy Acapulco.