I do not have experience with the net5501, but as for the vpn1411, you
may want to check out this thread:
http://marc.info/?l=openbsd-misc&m=117826557508813&w=2
It talks about recompiling the GENERIC kernel minus a few options, which
has the side effect of fixing SSH connection problems with the vpn1411
and the net4801. Why? I dunno. I'm not a developer, and my understanding
of C is roughly equivalent to the average English writing skills of
children in junior high.
Give it a shot, and please report back to the list if it fixes things
with the net5501 combined with the vpn1411.
Breeno