Site you mentioned provides opensource packages for HPUX.
Those are are not built by HP or supported, but work.
HP provides depot packages if you have support on :
Software Depot home
There is also a large number of open source depots there.
On HPUX 11.31 (datacenter edition) the mentioned command is available on the system under
/usr/sbin/userdbset.
This should be a depot, accessible from HP site if you have login :
PHCO_36480.UX2-CORE: /usr/sbin/userdbset
I would always suggest when patching to use quality pack patches (large bundles).
Rather then applying individual patches to system(s), if possible of course.
Read up on those here :
Patches: HP-UX
Hope that helps
Regards
Peasant.