Gotcha! So the DOA IG actually did an investigation of the DCHS access issue. Reading through the posts, I thought you had confused separate investigations.
The IG normally publishes a public report detailing the results of an official investigation. I take it the IG's office has been contacted and given no response. If no formal report has been issued, I do not know if the findings of the investigation would be subject to FOIA. I do know somebody who will want to find out.
Your observations about the Interior IG are consistent with what I've heard elsewhere. Mr. Earl Devaney works "At will" for Interior Secretary Gale Norton, and has been very careful not to criticize her or other high Interior or agency officials. This includes former Interior Solicitor (head lawyer) William Myers, who was accused of arranging a fraudulent BLM grazing deal with a politically-connected Wyoming rancher. Instead of criticizing Myers, the IG's report blamed a subordinate mid-level member of the Solicitor's staff. Coincidentally, Myers is a stalled nominee to be a federal judge on the 9th Circuit Court of Appeals.
By the way, Chief Ranger Nelson starts his new position, a demotion to Field Ranger in Craig, Colorado on or around September 15.