Thanks I was pretty sure that was how it worked. By support units do you mean artillery and hqs?
No, he means the support counters such as crocodile tanks, royal assault engineers etc. Artillery and HQs DO count against the 6 point stacking limit on the beach hex as per the stacking points on their counter (normally 1 for the HQs and 1 or more for the artillery).
Also, remember that HQ and artillery cannot land in enemy Zone of Control, so you need a beach hex clear of EZOC before they can land.