Not terribly credible. The reddit thread I first saw it on had a translated MoD announcement that only said Wagner were treasonous (but not shoot on sight) and some people arguing that the Russian version looked fake.
As a Russian, currently living in Moscow, can say this is bullshit. MD force other military volunteers squads to sign contract. Only Wagner Group declined.
The only tactic these guys know is escalation in the hope that someone backs down. Prigozhin as a gangster knows the value of intimidation and not backing down, but Shoigu is just hoping his credentials do the scaring for him because he has no fucking street cred, he's just some Ural paperpusher. I think he's terrified of prigozhin