Hi
It depends on the actual platform newer and older ones differ, catalyst switches pull there svi mac from cpu stash of them , some can be changed from the system mac svi , some not depending on the platform cant be overridden at all and will always be the same, usually no matter the platform when a mac address is given out every vlan interface gets the same one have a quick look at this doc with its link it explains how there given
https://supportforums.cisco.com/document/7816/mac-addresses-used-cisco-3750
