Claims are no good, especially when they're accompanied with "I heard". Instead of speculating, look at the proofs. Tupac wasn't a Muslim, Snoop joined the Nation of mIslam, who are a bunch of idiotic kuffaar... They're like a black version of the KKK. Akon is from Senegal, a Muslim country, yet he was foolish enough to use Al-Faatihah in his music.
You shouldn't worry about these idiots, Danyal is correct in what he has said. Majority of these rappers who apparently take shahadah just join the Nation, they worship men! Only a small group of them accept Islaam, and even fewer of them practice Islaam, namely Mutah 'Napoleon' Beale and Amir Junaid 'Loon' Muhaddith (and some others)...
May Allaah guide the first group, forgive the second and reward the third.