Hanging I'll say the opposite.
Yes, always trust your instinct if you feel or your child are in immediate danger. In a situation where a stranger is staring at you late at night on a train, it's best to take all precautions. It's also important to never put yourself in a vulnerable position (if you can help it) unless you are 110% comfortable.
However, studies have shown that gut instincts are only 50% reliable at best. Whether you realize it or not you are looking at the world through a lens of bias based on your own experiences, not a lens of objectivity. People that have been abused may be reminded of their abuse when people exhibit certain mannerism, but the person may be a decent person (no one is a saint). People that have been abused also learn to trust or gravitate to the type of people they grew up with because humans like familiarity.
I've known plenty of people I didn't like, got a bad feeling about, or generally felt uneasy about and they turned out to be decent people. There's also been people I liked who turned out to be assholes. And of course, there's people who I didn't like and they turned out to be jerks. But that doesn't mean your gut is reliable, it just means that of the people you remember feeling uneasy about you were proved right. But how many people have you felt uneasy about and were proven wrong?
One of my good friends and I didn't like or get along with right off the bat. We simply didn't like each other. She's one of my better friends who I trust. There's others I didn't like and simply saw no point in giving a chance, and that's fine too. They have other friends that do like them, and as with most people they have a few people who don't.
But no one is psychic. It is however important to look for signs. So if you notice a change in your son's behavior, or she does something other that "You don't like her" then yes remove him. It could be as simple as she's automatically on the defensive with parents who are constantly telling her how to do her job with their child, but good with children.
So yes, change nursery if you're uncomfortable and are unable to relax at work about it. But also remember, almost all cases of abuse cases are from people that are personal friends with the parents, not child workers.