Such awful advice. While it is entirely possible that Dad will be a loving grandfather, with non of the abusive behavior experienced by the female writer, it is quite far from a sure thing. Even saying to gramma that she never leave the kids alone with grampa is no guarantee...she has a very strong incentive (losing future access to her grandkids) to lie about any bad behavior that happens, and it is years before a child is old enough to speak for themselves. 

I do agree that kids should have some relationship with gramdparents. Seems to me that supervised visits when grampa is present is a reasonable limit. IF gramma wants a sleepover, she comes alone to the children's house.