I'm guessing the Covey contract pays him more than the normal 40-man minimum in AAA (a la Cave) to perhaps make it easier to get him through waivers (though that didn't work for the Orioles and Cave).
And what does that mean about Stubbs? That they can release him any time and not be on the hook for the $450M or does it become fully guaranteed once the season starts and that's just the normal situation.
Ah, answering my own question, the rules changed with this CBA. https://www.mlb.com/glossary/transactions/non-guaranteed-contract
A player on a split or Minor League contract will earn the prorated portion of his Major League salary for time spent on the Major League roster. Clubs can also sign players to non-guaranteed contracts but still place them on the 40-man roster. Those contracts become guaranteed upon the player making the Major League roster out of Spring Training, but he may also be cut prior to Opening Day. Players cut on or before the 16th day of Spring Training are owed 30 days' termination pay (based on the prorated version of his agreed-upon salary). A player cut between the 16th day and the end of Spring Training is owed 45 days' termination pay (based on the prorated version of his agreed-upon salary).
Per the 2022-26 collective bargaining agreement, arbitration-eligible players who settle with their teams on a salary for the subsequent season without going to a hearing will be eligible to receive full season termination pay, even if they are released prior to the start of the season (this rule will go into effect after the 2022 season). Previously, the salary for such players only became guaranteed if the player was on the Major League roster or injured list when the regular season began. Arbitration players who were cut before then would be owed either 30 or 45 days' worth of termination pay, depending on the point in Spring Training the player was released.