I've just watched the BFI (UK region 2) version and according to the commentary, yes, they are chamber pots. I suppose with so many guests a makeshift restroom was the only answer, even in a grand mansion. Not much room, though. I presume the ladies' restroom was larger with the pots more spread out to accommodate all those cinolines!
God, I was wondering that too - right there next to an open doorway into the ballroom - you'd think the servants would be a bit prompter about emptying some of them out...
Standards were simply different in those days. Look at the pictures of the White House during the same period. Not chamber pots, but dozens of spittoons everywhere. (At Versailles during Louis XIV's time they hardly used chamber pots, just in the corner.)
That's gross but I heard about that in a documentary. Watching the pots scene in this film made me think it must've smelled of urine so bad. Just imagine a gas station, yech.