The on-site news caster in the rehabilitation scene in Idiocracy is commonly identified as Mike Judge. A Reddit thread about the “Rehabilitation Announcer” says, “It’s Mike Judge from what I remember,” which matches the film’s behind-the-scenes casting discussion.

Quick note

The role is usually referred to as the rehabilitation announcer rather than a named character in the film’s credits, so this is one of those cases where fans often identify the voice/appearance by the actor instead of a formal character name.

Why there’s confusion

People sometimes mix up the announcer with other background broadcast voices in the movie, especially because Idiocracy uses a lot of satirical TV and news-style segments. That’s why you may see different guesses in forum posts, but Mike Judge is the most repeated answer for the rehab announcer.

TL;DR: Mike Judge.