No, it isn't. Once the police seize a large enough network of phones, all those id's are trivially correlated, even if they are ostensibly decentralized. If the capability exists to contact trace for epidemic tracking purposes, the capacity for abuse by law enforcement for mixing with bad actors whose id's are also known through device seizure also exists.
no, because you need to publish your data to do anything, which means they can't track anyone who's phone they don't have, and they can't track anyone who's details haven't been published.
So all the can actually track are people's who's phones they already have complete unlocked access to. At that point they can just read out the google and Facebook tracking data and subpoena them for the full information.
