Yeah it seems he used the Rick for Kill 'Em All and Ride the Lightning, and the Aria SB for Master of Puppets. But the fact that he used an Aria on Master of Puppets has no bearing on whether it was 'buried' or not. The bass just wasn't mixed very prominently. It would have been the same if it was a Rick. You can hear it if the bass is turned up (check all the Youtube clips nowadays)...Same with Jason on ...AJFA. It's not that his bass (a Steinberger according to the ...AJFA bass tab book) was somehow unable to record a decent sound on a recording, it was just turned down! I think Jason's bass tone is pretty wicked on ...AJFA.
As for the live shots with the Cliff, he used Aria 95% most of the time on the MoP tour, but would occasionally bust out the Rick for The Thing That Should Not Be...On live recordings, you can hear the Aria just fine. There are some nice soundboard recordings out there.