If all you want is a disk which just has NetBSD on it, you don't need
to worry about creating extra small partitions with pfdisk etc. I have
a disk with just NetBSD on it :

ST3660A|Automatically generated label:\
	:dt=ST506:se#512:ns#63:nt#16:sc#1008:nc#1057:\
	:pa#204624:oa#0:ta=4.2BSD:ba#8192:fa#1024:\
	:pb#122976:ob#204624:tb=swap:\
	:pc#1065456:oc#0:\
	:pd#1065456:od#0:\
	:pe#737856:oe#327600:te=4.2BSD:be#8192:fe#1024:

and it does work. (I keep emphasizing as everyone seems to say you
need a small dos partition on it to mystically make it work)
As it is entirely NetBSD, you don't need os-bs etc. What happens when
you write a disklabel using the whole disk to it, newfs it and copy
bootblocks to it? How does it fail? What is your disklabel?

Good luck,

Patrick