I'm seeing this same issue on a "new" (to me) Netra T1 AC200.  A couple
of interesting additions:

1. aceride0 (the on-board IDE controller supporting the CD-ROM) is also
complaining of lost-interrupt messages.  I presume this and the SCSI
timeout are caused by some system-wide interrupt routing issue.

2. The hardware is fine; OpenBSD 4.2 installed on it A-OK (I didn't have
Solaris media and wanted to verify that all system components were happy
before my eBay non-DOA warranty ran out ;)).

This was with a INSTALL kernel from a 2007-11-23 HEAD snapshot:

NetBSD 4.99.37 (INSTALL) #0: Fri Nov 23 07:40:58 PST 2007
builds@wb44:/home/builds/ab/HEAD/sparc64/200711230002Z-obj/home/builds/ab/HEAD/src/sys/arch/sparc64/compile/INSTALL