I don't think you can because the LTO is not a native AIX tape device, i.e. you need to load the atape driver to use it and this driver will not be available during boot.
If it can be used as an "other scsi tape" without the atape driver you may be able to do it, or if it is fibre attached the same may apply.
Check in SMS if the drive is listed as a boot device, or better still create a mksysb and then try to boot from it if you want to know for sure it will work.