Hypothetically, if you are a witness or whistleblower who's adversary was a very big corporation (such as boeing), what measures could you take to prevent yourself from being "suicided"?
Not necessarily. The only people who would need to know are the people who are already researching you to have you killed for a potential leak, and they would operate under the assumption of a DMS in place already.
Worth noting that this is something that can change over time. For example, if Snowden had done such a thing, it would be essentially useless now, since the known and accepted activities of the US government are now worse than what Snowden revealed.