Looks like here is a bug in this object: expecting ArrayOfSAMLAuthenticatorId which doesn't actually exist and should be just and array of SAMLAuthenticatorId.
A workaround is to create an object VMware.Hv.ConnectionServerSAMLData where you can just set this array
[VMware.Hv.SAMLAuthenticatorId[]]$saml_auth_array = $saml_auth_id
$saml_data = New-Object VMware.Hv.ConnectionServerSAMLData
$saml_data.SamlAuthenticators = $saml_auth_array
Then update the same way SamlSupport and SamlAuthenticator in the new object. Just take values from $csList[0] if you don't need to update them.
After that update the entire authentication.samlConfig key with $saml_data.
