It depends on what sent him there and how seriously the facility views the infraction relative to his treatment eligibility.
In many cases, a SHU placement does not automatically disqualify someone from a treatment program, particularly if the underlying incident was relatively minor and he has otherwise maintained a solid record. Treatment programs like RDAP in the federal system and similar substance abuse tracks in state facilities look at the full picture rather than a single incident in isolation. One trip to the hole for a minor infraction does not necessarily close the door.
Where it gets more complicated is if the infraction was serious, involved substances, violence, or behavior that directly contradicts the readiness for treatment that these programs are designed to assess. A drug-related incident for someone waiting to enter a substance abuse treatment program is a harder sell to the program administrators than an unrelated disciplinary matter.
The timing also matters. If he clears the hole and enough time passes before the treatment start date for his record to reflect the resolution, the impact may be minimal. If the SHU placement is still active or very recent when the treatment slot opens, the program may defer his entry until the disciplinary matter is fully resolved.
His case manager is the right person to ask directly. They know the specific infraction, the program's requirements, and whether the timeline is still intact. Encourage him to have that conversation with his case manager as soon as he is out of the hole so there are no surprises when next month arrives.