They flew alone. Nobody else acting as backup pilot.From your source:
On October 14, 1997, on the 50th anniversary of his historic flight past Mach 1, he flew a new Glamorous Glennis III, an F-15D Eagle, past Mach 1, with Lt. Col. Troy Fontaine as co-pilot. The chase plane for the flight was an F-16 Fighting Falcon piloted by Bob Hoover, a famous air-show pilot, and his wingman for the first supersonic flight.
I haven't been able to confirm whether Hoover was alone in the F-16. In any case, I doubt either one was performing high-G maneuvers during this PR flight.
This is all in response to the 74yo pilot that crashed at Reno and I posted the fact that Chuck Yeager also flew when he was in his 70's. Chuck Yeager radioed that he just passed mach 1.5 - HE passed mach 1.5 - there's no mention that LC Troy Fontaine did any piloting or flew the plane at any time. Yeager was flying the same flight profile he flew when he broke the sound barrier. The F-15D always carries two people. It's never flown solo. There was no reason to mention the LC in back. You fly the plane from the front due to limited forward visibility from the back. Piloting from the back is usually done in emergencies only and pictures show CY in front. As for Hoover, the plane he flew was listed as an F16 Fighting Falcon (called the Viper), not an F16/B the two seat version trainer which would of necessity have a second seat.No mention of anyone with Hoover.
Chuck Yeager wouldn't have done any high-G maneuvers since he didn't do it in the original flight profile.