FYI,

> Is the disklabel similar to the x86's MBR and Partition Table?

Disimilar.  They are different beasts motivated by different goals.

So called "BSD disklabel", which was introduced 4.3BSD-tahoe release,
is used for having multiple "UNIX-type" filesystems on disks.  Until
the introduction, there was no standard way to have disk space
management information on each disk.  Reason?  UNIX was distributed
with source codes and every user was expected qualified enough to
install the system for (then-) "mini computers" and to build & tailor
the kernel properly (been always major challenges for new comers.)
Kernel builders had to adjust and create disk geometry information
_IN_ device driver source codes themselves. 

Growing binary only distribution popularity, some of suppliers started
splitting site configurable "data portion" from rest of kernel
providing most of kernel in binary forms.

It's ackward and mis-approach to have disk geometries inside device
drivers.  SunOS invented its proprietary "Sun disklabel," while ULTRIX
did different thing controlled with chpt(8) command. 

Digital UNIX adapted tahoe disklabel.  It's compatible with NetBSD
(but it's rumored that DU ffs is proprietary extended and not fully
compatible with NetBSD ffs)

DOS partion table was designed to have upto 4 different disk space
segments (some call them 'slices' to distinguish UNIX notion of
'partitions' which store UNIX filesystems).  It allows to have
dissimilar filesystems for exotic OSes in a single disk storage.  If
MBR, a small store segment for PC's primary boot program, is capable
to detect and distinguish such segments smartly, users can boot the PC
choosing one of multiple OSes on the fly/fry. 

Tohru Nishimura
Information Technology Centre
Nara Institute of Science and Technology