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