> My next question is, do I (like as it is in linux) need a specially
> patched version of pppd to get this to work too?

Well - no.

There are two things we need to keep apart:

 - the rp-pppoe pkg
 - the in-kernel stuff

The latter does not need any pppd at all (it's doing everything in kernel).
This is what http://www.netbsd.org/Documentation/network/pppoe describes.
It does need a kernel with "pseudo-device pppoe" configured into it, and
nothing else.

The rp-pppoe pkg will work with the standard pppd shipped with current
(and I seem to recall it will automagically install a pppd pkg if used
on some older NetBSD version that does not ship a new enough pppd in tree.)
The rp-pppoe pkg will require a kernel with

  pseudo-device   bpfilter        8

(or some other small number instead of 8)

and it is all setup with adsl-setup. This has ~ nothing in common with the
setup described at above URL.

Martin