They do eat rattlesnakes!!! Had one on our ranch may years ago, it would go across the 12' wide senderos and it's head was on one side and it's tail on the other, it was around 13 or 14' in length.
I was bow hunting one morning and this monster came by me looking for a meal in a rats nest. I just about jumped outta skin when I looked down to see this thing go between my feet. I thought it would never get through going between them....I just froze after seeing that it was the Blue racer instead of a rattlesnake...it went on it's merry way and I decided to leave the area too, the next snake might be a rattler!