I don´t have any evidence,who this man was. But there were several Plenty Holes at Pine Ridge Reservation, so I suggest he could be Oglala. An Oglala Plenty Holes was born in 1876 and married in 1894; I think that age fits the man in the photograph, possibly taken by Herman Heyn around 1899.

See: http://freepages.genealogy.rootsweb.ancestry.com/~mikestevens/2010-p/i51.htm#7340

(?) Plenty Holes was also known as (?) Wasun Ota. He was born in 1873. He married Mary (?) circa 1894(?) and was listed as Head of the Household on the Indian Census at Pine Ridge Indian Reservation, Wounded Knee District, Shannon Co., South Dakota, USA, on June 30, 1904. — Dietmar Schulte-Möhring