By default OpenBSD will recognise the Apple USB SuperDrive, you just cannot insert a disk. The drive doesn't seem to be an "ready" state. Sending the right SCSI command to the drive, will allow it to accept a disk and read it as you would expect.
Use dmesg to find the device name, most likely it will be cd0. SCSI commands needs to be sendt to the raw device (and partition c, meaning the entire "disk"), so /dev/rcd0c in the case of our SuperDrive being cd0.
The following scsi will send the "unlock" sequence to the SuperDrive, allowing it to accept disks
$ doas scsi -f /dev/rcd0c -c "EA 00 00 00 00 00 01"
You can now use the drive normally, and use the eject command to remove the disk.