Alrighty. I was just a tad confused what you were envisioning... 

Anyway, I'll be glad to offer suggestions.

Dredges prefer easy prey and will ideally seek out things that will not fight back like all predators. Four of them headed towards the Inn because they believe they would have an easier prey. Arco and his group have already killed quite a few of them so he has already been deemed as difficult and dangerous. Those at the inn that they saw, might be easier. It isn't so much fear as it is convenience. So using an illusion of something like a sheep? Well that could draw them. They either need to see it or smell it. 

You could also throw out some stinky, rotten food. Being already undead, they'll love the smell and taste of rot.