There are no accepted Harney County records in the eBird database, probably because the few submitted records were marked with an X with no supporting identification details in the comments section and observers did respond to queries for more information. If there are written descriptions, photos and/or recordings, I could log it under the "Historical Harney eBird" account. Feel free to contact me privately or point me in the right direction.
I worked several seasons working in the S Cascades along the Jackson/Klamath County line and searched quite a bit for Hutton's Vireo unsuccessfully. I suspect the best place in the county is the Lower Klamath River canyon just above the CA state line.