How can i create new users in vSphere.local using powercli?
Not via a cmdlet or an API method I'm afraid.
But you can use the dir-cli command (eventually through an SSH session or the Invoke-VMScript cmdlet), see William's post vCenter Server 6.0 Tidbits Part 9: Creating & managing SSO users using dir-cli
Blog: lucd.info Twitter: @LucD22 Co-author PowerCLI Reference
Is this still accurate?
No, there is now the VMware.vSphere.SsoAdmin module that contains the New-SsoPersonUser cmdlet.
See also New Open Source PowerCLI Module for managing vCenter Single Sign-On (SSO) - VMware PowerCLI Blog
Blog: lucd.info Twitter: @LucD22 Co-author PowerCLI Reference
Thank you and it can also be obtained here.