Three of many mythological entities in Dante's Inferno are Charon, Cerberus, and harpies. Charon is the demon ferryman who takes souls, as well as Dante and Virgil, into Hell. Cerberus is a three-headed dog that guards the third circle of Hell, and feasts on the bodies of gluttons. Harpies are found on the seventh circle of Hell. They are women with the bodies and talons of birds. There, they torment the souls of those who have committed suicide, which have been turned into trees, by using their talons to rip the suicidal souls's leaves and branches.
Charon is depicted in many Greek and Roman stories, but Virgil's Aeneid provides a description of Charon that most resembles the demon described in Dante's Inferno. Both Virgil and Dante refer to to Charon as having flaming eyes. Similarly, Cerberus appears in a number of mythological pieces, but he is introduced by Homer as a creature that Hercules must capture as a way to prove himself. Harpies are described by a number of poets, but Hesiod introduces them in his Theogony as winged maidens. Only in later descriptions do they take their more monstrous form.
Given that all of these creatures inhabit Hell, we can infer that Dante saw them as lesser to the Judeo-Christian religions. Further, they all serve a purpose in doing God's bidding, and it is through invoking God that Virgil is able to convince Charon to carry them across the river to Hell. As such, these mythological creatures serve as pawns in the larger Divine Comedy. They are subservient to Dante's one true God represented in Catholicism.