Ok; first, it's totally normal for kids to pull this behaviour at pick up. It's a way to "tell" mom and dad that they're pissed about being left at daycare (whether it's concious or unconcious). At the end of the day, most kids are tired and overstimulated and this is how it tends to manifest.
Having said that.... it's not okay!! I have a paragraph in my handbook that talks about this sort of issue. Your best behaved child can turn into a little monster when mom/dad show up at the door, but that is NO reason for the behavior to be ignored or allowed.
My handbook states that when a parent arrives, THEY are now in control of their child and THEY are expected to enforce MY house rules. However, if they won't.... I damn sure will!! I came to this conclusion the day that a little boy kicked my front door into the wall at pick up, because he didn't like what dad told him they were having for supper! (I am sorry that I tell that story so often, but it was a real defining moment)
No, it's not okay to stomp around, scream and yell, or generally disobey the normal expectations. And perhaps if you harden up a little, the parents will see that they do, indeed have (or should have) some control over the situation. Start enforcing the rules and consequences. This is how we, as providers, can help to "teach" the parents what we feel needs to happen.
I often wonder if parents are embarrassed to discipline in front of me? Like I might judge them for it? Let me tell ya... I judge them a lot more for NOT disciplining!! LoL