The videotape was sent anonymously to WRCB-TV, Chattanooga, and shows a Phi Delta Theta member shooting bottle rockets into the pants of another fraternity member too intoxicated to notice.
The alleged prankster then bragged on a Facebook page he lit four bottle rockets without his fraternity brother awakening.
A second Facebook post shows a lewd act performed on another unconscious fraternity member, the television station said.
"We take it very seriously," school spokesman Chuck Cantrell said, adding the investigation concluded the actions on the videotape did not meet the definition of hazing, which involve "distress put upon a person as a factor of membership."
He said the investigation revealed the acts were performed by alumni who returned to the fraternity house for a homecoming weekend.
The alumni in the video could face criminal charges, but none has been filed, the television station said.