Eminem is Eminem. NWA is NWA. There's two different things there. For example, let's take the first track on Em's album, "I'll Kill You": that's custom made for him. It wouldn't work for Snoop. These two things don't mesh at all. Niggaz Wit' Attitudes could not have Eminem in the group. The Public would fking lose it.

Marshall Bruce Mathers III was born on the 17th October 1972, Kansas City, Missouri, USA. Son of a fifteen-year-old mother at the time of his birth and a father who left six month later never to return, Marshall spent his early childhood being shoved back and forth from Kansas City and Detroit. He settled on the Eastside of Detroit when he was 12. Switching schools every two to three months made it difficult to make friends, graduate and to stay out of trouble.
Being a rap fan for most of his life, Marshall began rapping at the early age of 4. Rhyming words together, battling schoolmates in the lunchroom brought joy to what was otherwise a painful existence. At the age of 14, he began to get very serious about his rapping but it wasn't until he was 17 that he actually made a name for himself, becoming M& M, which he would later respell as "Eminem".
Being rejected by most fellow rappers because of his race, Marshall grew an anger that flows through his music to this day. After failing the 9th grade for three times in a row, he quit school, but remarks that he doesn't consider himself stupid and doesn't advise that people should follow his example. He says that it just wasn't for him. Forcing himself on radio shows, freestyle battles, Marshall threw himself head first into the rap game, where he was swallowed up most of the time.
His very first album was titled "Infinite" and, while the album sold less than a thousand copies, it was the gearing up stages for the rapper who became a millionaire. It was then that his daughter, Hailie Jade Scott, was born on December 25th of 1995 with long time girlfriend Kim Scott.
Having nothing to lose at all, flat broke and not knowing where he would be living the next week, Marshall set out to rant about life in general, the set quickly caught the ear of hip-hop's difficult-to-please underground. What came out of this was the Slim Shady EP, the early work for the later Dr. Dre revised Slim Shady LP.
Down to nearly his last dime, he went into the 1997 Rap Olympics in Los Angeles, basically hoping to win the $1,500 cash price which he badly needed. After battling for an hour and throwing back every race diss thrown at him, Marshall made it to second place losing in a slip up. Furious that he had lost, Marshall didn't even notice that he had been spotted.
In the crowd were a few producers from Interscope, and they were handed a copy of the "Infinite" tape by way of a demo. Dr. Dre got to hear it and eventually tracked him down. The two instantly hit it off, recording four songs in the their first six hours of working - three which made it to his first LP. 
After the album was finished, Dr. Dre asked Marshall to come work with him on his new album. He helped produce several tracks and was on the best songs of the album. Now officially making it, Marshall and Dre set to make his second LP. The album became the Marshall Mathers LP and won 3 Grammies and was the first rap album ever to be nominated "Album of the Year", selling more than 8 million records in the United States alone.
He also stunned critics when he shot down all homophobic remarks by performing "Stan" with Elton John. Currently working on his third LP, Em has made a movie, 8 Mile (2002), and has gone back and brought his friend with him; D-12. Though 2001 was a rough year for the rapper, being charged with weapon offenses, divorcing his wife, and almost going to prison, Marshall explains his life today in one word....  Better!