> To be honest, I wouldn't mind knowing if you can label the disk without 
> partitions, except maybe d. I've never tried it, and I can't find 
> anything in the man pages.

If you mean, can you have the d partition be the only one, it works fine.
Just tried it:

# /dev/rsd0d:
type: SCSI
disk: EZ135
label: /mnt
flags:
bytes/sector: 512
sectors/track: 32
tracks/cylinder: 64
sectors/cylinder: 2048
cylinders: 128
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0		# milliseconds
track-to-track seek: 0	# milliseconds
drivedata: 0 

4 partitions:
  d:    262144   0         4.2BSD     512  4096    13