can a unionized blameless, hardworking employee claim constructive dismissal after 4 years of harassment, discrimination, false accusations, intentional infliction of mental distress, assault and battery, conspiracy from employer to find cause to terminate

First of all, if it is as you say it is, this is a matter for the police, not an employment matter. Constructive dismissal doesn't really exist in a unionized environment. That said, there are a number of things the union can grieve. If you are part of a union, you must go through the union and cannot really do anything on your own, even if the union refuses to help. With a union you have take the good as well as the (very) bad.