I know that unlocking bootloader does wipe the /data partition. However, can it also wipe the /storage partition and others, too?
It wipes the complete storage when the bootloader has never been unlocked. If it has been unlocked it just wipes /data as far as I have experienced this on my oneplus x. (Onyx)
There is nothing like storage partition. What you see under /storage/emulated is a FUSE implementation of /data/media/userID. Whenever you unlock or relock the bootloader, fastboot causes factory reset of the device which wipes data and cache partitions. No bit of data escapes it, including what you see under /storage.
printf("oem unlock requested:\n"); printf("\tUnlocking forces a factory reset and could\n"); printf("\topen your device up to a world of hurt. If you\n"); printf("\tare sure you know what you're doing, then accept\n"); printf("\tin %d seconds via 'fastboot oem unlock_accept'.\n",