While it is not necessary, it is recommended that you get rid of the 'UUCP' users. [uucp & nuucp]
Since they belong to a 'system' that is RARELY used.
You do this by executing the 'pkgrm' command for the two UUCP packages: SUNWbnuu && SUNWbnur.
Which (respectively) are 'Basic Networking Utilities (User)' and 'Basic Networking Utilities (Root)'.
[Remove in that order.]
They are usually considered security risks, and are really not much use unless there is a modem attached to the computer.
The 'nobody && noaccess' users are sometimes used as IDs to run certain processed as, to make the processes less likely to cause harm if 'hacked'.
Netscape used to run the 'httpd' as 'nobody' by default, some folks run Apache as that user.
The 'smmsp' user is what sendmail runs it's 'listen' process as, and the 'listen' user is a left over from the AT&T System V Release 4 OS (which was the original 'root OS' that Solaris grew out of).
The 'listen' user no longer is used, BUT, as you said, there might be 'stuff' lingering around that requires it.