Assuming I have 2 roles set up:
rid 1 = 'Customer'
rid 2 = 'Management'
$newUser = array(
'name' => $name,
'pass' => $password,
'mail' => $mail,
'status' => 1,
'roles' => array(1 => 'Management'),
'notify' => 1
$user = user_save(null, $newUser);
The above code would still validate and assign the customer permission to the user although the role title does not match the role id.