I would not say 65534 is a ridiculously high number. It is not that much negative (the standard doesn't states if uid_t is 16 or 32 bits nor does it says if it is signed or unsigned) and still pretty low compared to Solaris allowed range. I would probably only object if useradd had picked 2147483647, the highest user id number supported by Solaris. I'm perplexed by 65534 having been chosen in your case, given the fact it should have been already set as the legacy NFS anonymous user.
In any case, I do not reproduce what you describe:
# cat /etc/release
Oracle Solaris 11.1 X86
Copyright (c) 1983, 2012, Oracle and/or its affiliates. All rights reserved.
Assembled 19 September 2012
# tail /etc/passwd
webservd:x:80:80:WebServer Reserved UID:/:
postgres:x:90:90:PostgreSQL Reserved UID:/:/usr/bin/pfksh
svctag:x:95:12:Service Tag UID:/:
unknown:x:96:96:Unknown Remote UID:/:
nobody:x:60001:60001:NFS Anonymous Access User:/:
noaccess:x:60002:60002:No Access User:/:
nobody4:x:65534:65534:SunOS 4.x NFS Anonymous Access User:/:
pkg5srv:x:97:97:pkg(5) server UID:/:
# useradd foo
# tail -2 /etc/passwd
This is consistent with Useradd manual page that states: The UID defaults to the next available (unique) number above the highest number currently assigned.