Yes there is a problem with the adduser in both A/UX 2.0 and A/UX 2.0.1.
When adding users in interactive mode the first available UID>=1000 is
used. But if an entry in the /etc/passwd has a UID>=1000 and the password
field is empty (for example, tom::1007:50:Tom van
Peer,ois,,:/users/tom:/bin/ksh), this UID is used for the new user.
This has been fixed in A/UX 3.0.