Direct proof of use
The AH-64E Apache is directly documented in the anti-ISIS campaign through U.S. military imagery and unit reporting from Iraq in 2017. A DVIDS image taken at Camp Erbil on January 10, 2017 identifies a U.S. Army AH-64E from Bravo Troop, 4th Squadron, 6th Cavalry Regiment, Task Force Saber taking off for an air mission request and says U.S. Army aviation was enabling partnered forces with battlefield air support.
A second DVIDS image taken at Erbil on July 11, 2017 identifies an AH-64E Apache from 4th Squadron, 6th Cavalry Regiment, Task Force Saber and states that the aircraft provided reconnaissance and attack capability in the fight against ISIS for Combined Joint Task Force - Operation Inherent Resolve.
Sources: Task Force Saber Air Mission, AH-64E Apache OIR
Timeline
On January 10, 2017, Task Force Saber AH-64E aircraft were photographed departing Camp Erbil for an air mission request as part of the coalition air-support mission.
By July 2017, DVIDS reporting described 4th Squadron, 6th Cavalry Regiment as equipped with AH-64E Apache helicopters and supporting Iraqi security forces with fires. The same reporting described the AH-64E as one of the fires platforms used in tandem with RQ-7Bv2 Shadow reconnaissance and surveillance aircraft.
Sources: Task Force Saber Air Mission, Task Force Saber Initiative, AH-64E Apache OIR
Narrative
Task Force Saber placed the AH-64E inside the coalition's Erbil-based aviation support to Iraqi and partner forces. The documented roles were not limited to aircraft presence: the source material connects the helicopters to air mission requests, battlefield air support, reconnaissance and attack capability, and fires support.
The clearest unit-level description came from DVIDS reporting on 4th Squadron, 6th Cavalry Regiment. It described the squadron as an enabling force for the coalition, said it supported Iraqi security forces with fires, and identified the AH-64E Apache as part of the fires-platform package used with Shadow reconnaissance and surveillance aircraft to find and strike ISIS personnel.
Sources: Task Force Saber Initiative, Task Force Saber Air Mission, AH-64E Apache OIR