Eminem is one of the rare rappers today who does not use much autotune in the studio or on the stage, except for a few phrases in some songs to mock other rappers or simply create funny parts. That said, like most artists, he might be using very subtle pitch correction in the studio when he sings high notes in some songs.
Eminem is one of the best and most famous rappers with his unique rapping, singing, and recording style. He never relies on autotune but uses different effects on his voice, like reverberation and different recording techniques such as layered choruses to make the songs sound better.
He records the same chorus singing in different octaves and styles and puts them all together to create a fuller and better-sounding choruses. But, when he raps live, he does not rely on these techniques and sings naturally.
He likes to use many effects on his voice as well as singing in different styles. But, he never relies on autotune and makes fun with singers and rappers who are dependent on autotune to perform, as can be seen in his song Tone Deaf.
He sometimes uses the autotune effect to mock other singers as well or just to create some funny parts in his songs. But, he does it in a funny, highly obvious way, and these phrases are often very short.
Also, in some of his songs, like Not Afraid, he probably uses pitch correction as he needs to sing very high-pitched notes. They are not very obvious, and it is not sure that he uses pitch correction, but in his live performances, he sings those verses in a lower pitch or gets help from backing vocals, avoiding hitting those high pitch notes.
For example, in the studio recording of Not Afraid, the high-pitched outro of the chorus is sung by Eminem. However, in the live version, he gets the help of the back vocals and backing tracks to sing the part.
In short, Eminem’s singing is entirely natural in live performances and almost entirely natural in his recordings. The talented artist uses many effects, including autotune occasionally, to play and have fun with his music, but is not dependent on them to sing or rap.