Pluto [Plouton], magnanimous, whose realms profound

 are fix’d beneath the firm and solid ground,

In the Tartarian plains remote from fight,

 and wrapt forever in the depths of night;

Terrestrial Jove [Zeus Khthonios], thy sacred ear incline,

 and, pleas’d, accept thy mystic’s hymn divine.

Earth’s keys to thee, illustrious king belong,

 its secret gates unlocking, deep and strong.

‘Tis thine, abundant annual fruits to bear,

 for needy mortals are thy constant care.

To thee, great king, Avernus is assign’d,

 the seat of Gods, and basis of mankind.

Thy throne is fix’d in Hade’s dismal plains,

 distant, unknown to rest, where darkness reigns;

Where, destitute of breath, pale spectres dwell,

 in endless, dire, inexorable hell;

And in dread Acheron, whose depths obscure,

 earth’s stable roots eternally secure.

O mighty dæmon, whose decision dread,

 the future fate determines of the dead, 

With captive Proserpine [Kore], thro’ grassy plains,

 drawn in a four-yok’d car with loosen’d reins,

Rapt o’er the deep, impell’d by love, you flew

 ’till Eleusina’s city rose to view;

There, in a wond’rous cave obscure and deep,

 the sacred maid secure from search you keep,

The cave of Atthis, whose wide gates display

 an entrance to the kingdoms void of day.

Of unapparent works, thou art alone

 the dispensator, visible and known. 

O pow’r all-ruling, holy, honor’d light,

 thee sacred poets and their hymns delight:

Propitious to thy mystic’s works incline,

 rejoicing come, for holy rites are thine.

The Lord of Hades is often called by the same name as his realm. He is not just the lord of the dead however. He is also the lord of the treasures under the earth and so is known by the alternative name of Plouton (the wealthy one). He is also called Chthonian Zeus (or Zeus of the Underworld) indicating his relative importance in the scheme of things. In the Orphic Hymn he is called the judge of the dead instead of the three judges of other myths. This is something that is one of the differences between the Orphic scheme of things and the classical mythology. 

This hymn seems to be focusing on his role as ruler of the underworld, but states similarly to his sister Hestia that “mystics” and “holy rites” are his. There was probably not much cultus to him in the sense that we think of it, but I feel that it is likely that he was paid cultus along with the ancestors of the family as he was now their governor and would be the one who would allow them to return to haunt the family that did NOT give them their proper remembrance.

Although there is not a KNOWN festival honoring him, I personally believe that there were observances honoring him that may have been part of the mystery cults. This is due to the fact that those who participated in the mysteries were supposed to have a favored place in the afterlife.