Are there any known problems with the Adaptec 1542 controller on
   NetBSD-1.0?

None that I know of.  I have a 1542B is one of my development
machines.

   Often, when I boot
   up, I get bizzarre filesystem errors.  The general complain is about a
   "non-media failure".

That's your drive reporting an error.  Unfortunately, the 1.0 kernel
didn't actually output the sense info.

Have you triple-checked the termination?