Ombudsmen will work if they truly feel they have independence and they don't have somebody telling them who to investigate and who not to investigate, except for the legal concerns you've outlined.
The military ombudsman has a lot of latitude in what he looks at, but he's stymied by the fact that he can only look at cases to a particular year and nothing before that date, which I think is wrong. Should the ombudsman for Veterans Affairs be able to look at all issues, regardless of the date?