Had this too:
What you get on the OCZ website is an ISO, not a DMG.
Here's the correct download of the firmware-updater:
And here are the correct instructions:
Go to page 4:
Under Mac OS X, do not use any third party utility. To put the required files on your USB flash drive:
1 Open Disk Utility and insert your USB flash drive.
2 Select the USB flash drive and click the Erase tab to display it.
3 Select format MS-DOS (FAT) and click Erase.
4 Double-click the.ISO file to mount the ISO image.
5 Use drag-and-drop to copy all the files from the mounted ISO to the USB flash drive.
Insert the bootable USB flash drive and start up your Mac.
Immediately after the chime, or when the screen switches on (indicated by the black screen becoming gray), hold down the Option (Alt) key until the bootable drives are listed. When using a USB flash drive, a USB icon (example below) is shown. This can take from several seconds up to several minutes: you must continue to press the Option (Alt) key.