Fights and bullying happen in jail the same way they happen anywhere people are packed into close quarters with limited outlets and high stress. It would be dishonest to tell you otherwise. But the degree to which your son encounters either depends largely on how he carries himself from day one.
Inmates who keep to themselves, mind their own business, and show basic respect to the people around them move through the environment with far fewer problems than those who draw attention to themselves, get drawn into drama, or disrespect others accidentally through ignorance of the unwritten social rules. Those rules are not complicated. Do not cut in line. Do not touch other people's property. Do not insert yourself into conversations you were not invited into. Pay attention to your surroundings and stay out of situations that do not involve you.
The population in a county jail tends to turn over more quickly than state prison, which generally keeps the culture less entrenched and the dynamics less dangerous. That does not eliminate risk, but it does mean the environment is typically more manageable than what people picture when they think of incarceration.
Boot camp is a legitimate path worth pursuing seriously. It is physically demanding and structured, but it gets people home faster and gives them something constructive to focus on while inside. Encourage him to pursue that option through his case manager or attorney as early as possible.
The best protection he has in there is his own behavior. Go in humble, be respectful, and stay invisible. Those three things handle most situations before they start.