Expectedly, zombies appear stupid; they break through the cab to get the luggage and can't properly put Frankenstein together. During their performance as humans to scare Mavis into not wanting to leave the hotel again, they blundered quite a bit; one briefly lost his head, another got pitch-forked through his head and the rest continued the charade even when lit on fire. They didn't even notice Jonathan following them through the tunnel, even with his scream from falling into the tunnel.
Perhaps rigor mortis is not the most desirable characteristic that comes to mind when considering hiring someone, but Dracula has found that zombies make loyal employees, even if they move at a painfully slow rate. The zombies do Dracula's bidding, no matter what he asks of them and no matter what the risks: bellhop services may involve a zombie losing a limb when trying to lift heavy luggage, and posing as threatening humans may cause them to end up in flames.
The zombies assisted Dracula in operating a fake human village to scare Mavis while some of them posed as humans.