They’re hiding their identities likely for several reasons:

• Some are almost certainly not even government employees.
• A fair number probably belong to known right-wing terrorist orgs.
• Some of them are “closeted” neo-nazis who don’t want people in their communities to know that they are neo-nazis.
• They fear retaliation for their blatantly illegal actions. Inaction by those with power to help is forcing the populace towards violence as the only means to justice. Also, underground resistance networks have historically conducted assassination of ranking members of occupation forces - they hope that this will protect them from the inevitable consequences of their actions if they succeed in holding onto power and unmaking the last vestiges of democracy.
• Concealing identity provides similar deniability for their heinous actions to that of firing squads and other executioners. This makes it easier for them to excuse their actions as “just following orders” (you know, the perennial nazi defense to avoid accepting responsibility for their own actions).
• Concealing their identity is part of the terrorism. If it’s not possible to know who these people are, they could be your neighbors, or schoolboard members, or even family. This uncertainty is intentional to try to keep the populace in fear of retaliation of exercising their Constitutional rights or resisting. (ie, if your neighbor is an ICE neo-nazi and you don’t know, they can inform on you to their superiors, if they see you leaving for/arriving from a protest).