Add admin account remotely
You are looking for the dscl command.  You can do it through ARD unix command to multiple machines at once, or send via ssh per machine. There's lots of discussion and great information here - What steps are needed to create a new user from the command line?

To summarize those answers, here's a quick admin user addition.

dscl . create /Users/corybohon

dscl . create /Users/corybohon UserShell /bin/bash

dscl . create /Users/corybohon RealName "Cory Bohon"

dscl . create /Users/corybohon UniqueID 503

dscl . create /Users/corybohon PrimaryGroupID 1000

dscl . create /Users/corybohon NFSHomeDirectory /Local/Users/corybohon

dscl . passwd /Users/corybohon PASSWORD

dscl . append /Groups/admin GroupMembership corybohon


A logout or restart will be needed for the user to show as admin in the System Preferences.

On a side note, I am not sure if this still works with Yosemite, but MagerVelp has a app called "CreateUserPkg" that can be used to deploy users.  CreateUserPkg, I use it with our MDM solution to push users as a pkg.

Terminal 101 full guide from above.