Creating a new user account using iCloud password
The linked iCloud/OS X Password feature appears have been removed in 10.11.4
The Change Password Dialogue box used to ask if you wanted to link your iCloud password with your account, now it goes directly to "Old password/New Password"
I ended up using steps 1-6 on this website.
Basically in single user mode in the terminal I ran:
mount -uw
rm /var/db/.AppleSetupDone
shutdown -h
I then set up the iMac using the other account I wanted to create.
While this isn't an ideal solution (and may bring some other issues?) it works until Apple fix this issue.