Yes, and this is one of those situations where being in the hole is actually the best possible outcome given the circumstances.
The hole, or segregation unit, serves two very different purposes that most people on the outside do not realize. It is used as punishment for rule violations, but it is also used as protective custody for inmates whose safety cannot be guaranteed in general population. When your son told staff he was scared for his life, he was essentially asking to be checked in, which is the inside term for requesting protective custody. That request was heard and acted on.
In protective custody he is physically separated from the general population, which means separated from whoever was threatening him. He is in his own space, staff are monitoring the unit, and the gang members who frightened him cannot reach him there. It is not comfortable and it is not easy time to do, but he is safe in a way he was not before he spoke up.
The harder reality is that this placement may last a long time. Once an inmate is checked into protective custody for safety reasons, returning to general population at the same facility is often not viable. The threat does not disappear just because he is separated from it. Facilities typically handle this one of two ways: keeping him in protective custody for the duration of his sentence at that facility, or transferring him to a different facility where he does not have the same enemies.
The fact that he recognized the danger and asked for help before something happened was the right call. It took courage to do that inside, where asking for protection carries its own social cost. He made the smart decision.
Stay in contact through letters and calls if he has access. Knowing someone on the outside is paying attention matters more than you might think.