Most likely yes, and here is why.
A violation sentence is fundamentally different from a standard sentence in how the system views it. When someone is released on parole or probation, the court is extending a form of trust, an acknowledgment that the person can reintegrate before their full sentence is complete. That early release is a gift, even if it does not always feel that way. When that trust gets violated and the person ends up back in front of a judge, the court's patience is significantly shorter the second time around.
Judges handing down violation sentences typically structure them to be served without the same good time credits that apply to original sentences. The reasoning is straightforward: good time is an incentive for people who are demonstrating they can follow the rules, and a violation of supervision is evidence that the previous incentive structure did not work. Some states have statutory provisions that limit or eliminate good time credits on VOP sentences specifically for this reason.
Whether he can earn any reduction depends on the state, the specific terms the judge put in the order, and the facility's policies. But the baseline expectation should be that he serves the full year. If any credit is available it will be modest, and banking on early release from a violation sentence is not a safe assumption to plan around.
The most constructive thing he can do with that year is treat it as an opportunity to come out in a genuinely different position than the one that led to the violation. Clean record, completed programming, solid release plan. That is what makes the difference when he is back in front of the system again.