At the start of his four-year long saga to complete the Sistine Chapel ceiling fresco, Michelangelo actually employed a small team of big-name Florentine painters to assist him with various tasks, however, he gradually phased them out as the painting progressed, thanks to differences in opinion, heated arguments, the likes. "Normal" Michelangelo things. However, he most certainly had a few assistants to assist him with the more menial tasks such as mixing the plaster, moving the scaffolding and such. The thing about a boun fresco (true fresco) is that the paint has to be applied to wet plaster to ensure a more lasting fresco. This means only a small section of a boun fresco can be worked on at a time (the area of the fresco which you can paint before the plaster dries) therefore he would had very little use to an army of assistants if he didn't want them to actually paint.

If you want to read more on Michelangelo or the inner workings behind his artwork, I highly recommend Michelangelo: The Artist, The Man and his Times