It’s an African American folk magic practice, but not specifically a religion. Most people who practice Hoodoo identify as Christian, however rootworkers can be of any religion. It does often incorporate the use of the psalm and saints though, so most practitioners come from a Judeo-Christian belief system.
Sometimes it’s confused with Voodoo, which is most certainly a religion. But the only thing the two have in common are some practices descended from African traditions. Where Voodoo has “lois” (deities) they worship, Hoodoo does not. Hoodoo was influenced by West African traditions, European grimoire magic, Native American spirituality, and Spiritism.