I wouldn't create another account with a uid of 0. My solution to this would be to install sudo and grant user accounts the amount of privileges they need. If a user account needs full access to do everything that root can do sudo will allow this functionality. Sudo also has a nice audit trail because it logs to syslog.
That is a very risky and unneeded solution to a problem which probably doesn't even exist. Look into RBAC control, also available in Solaris 9 to my knowledge. In other words: simply create a regular useraccount and grant it all the privileges it needs.
Better yet: create a role for root-alike administration and allow certain accounts to log into this role.
As a sidenote, even though I am paranoid where security is concerned, I really would be very carefull with programs like sudo. Sudo is in the end nothing more than a program which is set SUID root and allows some form of controlled access. But due to its SUID bit this also involves quite some risk and Solaris' own RBAC control is much more flexible and robust for attacks.