Chokhamela, the Untouchable Mahar, along with his wife, her brother, and their son are all historic figures in the Warkari cult. The sixteenth-century Brahman poet, Eknath, wrote more than forty poems as if he were a Mahar, underlining their importance to the everyday world of that time.There is mention of Chokhamela even in the Guru Granth Sahib of the Sikhs.
I also spent a lot of time trying to locate the reference in Sri Guru Granth Sahib Ji....unsuccessfully. There is not doubt that Chokamela, the historical person, was an influence in the Bhakti movement of Northern India. However so were many other "sants" who do not achieve mention in Sri Guru Granth Sahib Ji.
To add: Chokamela was a disciple of Bhagat Naamdev. I decided to narrow my search to the bani of Naamdev, and could not find mention of Chokamela there.