You boot from the spot, so all you need to have is a mksysb image .. you dont need a bootable mksysb ..
The spot must be at at least the same ML level as the mksysb you are going to restore.
With a 5.3 NIM server you can define the mksysb resource on the master and give it the client to backup and it will nfs mount the filesystem and run the mksysb for you ... not sure about 5.2 NIM server tho as I havent got one
to use that mksysb to restore a client .. you need a spot / bosinst / lpp_res / mksysb .. allocate them as network resources to the client, then perform bos_inst operation on the client and then select "Source for BOS Runtime Files" --> pf4 --> mksysb ..
as long and the spot and lpp_res are at the right level the install will start ..