Your rights don’t stop because you work for the government. It is up to the state to prove its case.
Flynn cooperated with the state and it cost him about a million dollars to avoid a life sentence, even though he was completely exonerated after the trial. The Democrats have gone 100% Soviet and are not the least bit concerned about anything, but getting them.
Secondly, I agree with you 100% about the danger of the process. But that actually makes the case against taking a Federal job in the first place.
Keep in mind that pleading the Fifth doesn’t mean you don’t have to testify. It just means that you can be compelled to testify after you’ve been given immunity against criminal charges. So you still face the prospect of a rigged political/legal process anyway. Oliver North is a better example than Flynn in this regard ... because that is exactly what happened to him.