Unable to retrieve users from AD on VMWare vcenter

I have no experience with the vma, but I suppose it has the vmware Perl SDK installed for you (according to this post virtually ghetto it should). In it you have lots of utils and I think this one is the one you are looking for:

vidiscovery.pl

If you do not wish to enter the credentials every time, then you need to setup the credendial store first.

[edit] Actually, I just tried it and while it kind of works, it is very slow because it gets all the info about every entity. Not very efficient. So I just wrote a very small script and this is all it takes:

#!/usr/bin/perl

use strict;
use warnings;

use VMware::VIRuntime;

# read/validate options and connect to the server
Opts::parse();
Opts::validate();
Util::connect();

my $vm_views =
  Vim::find_entity_views(view_type => 'VirtualMachine',
                       properties => ['name'], );

foreach  my $view ( sort @$vm_views) {      
  print $view->{'name'}, "\n";
}

# disconnect from the server
Util::disconnect();                                  

This presupposes that you have a $HOME/.visdkrc file in place with the correct info:

VI_PROTOCOL=https
VI_SERVER=fqdn
VI_SERVICEPATH=/sdk
VI_USERNAME=username
VI_PASSWORD=pwd

And as you said you have the vma, all the libraries should already be there for you. This script gets me all the vm's (just their names in under 1 second). If you do not have a CA in place and your virtual center has a self signed certificate you should set this envvar first or the Perl lwp library will bomb out when running the script:

export PERL_LWP_SSL_VERIFY_HOSTNAME=0

You can't manage ESXi 6.5 hosts with vCenter Server 6. You need to use vCenter Server 6.5.

http://partnerweb.vmware.com/comp_guide2/sim/interop_matrix.php?#interop&2=&1=