Ryan,

You are having packet collisions. Unfortunately to operate effectively on a multi vlan network like this you'll need to be using Layer 3 or higher switches.

In effect, Artnet is such a dumb protocol that Catalyst seeing misc packets from other devices and it's interpreting those as legitimate data.

Try changing the gateway address of the hog to itself and then change the gateway address of the Cats to the hog as well. This won't mean anything but it will make the Cat ethernet adaptors thing that routing needs to go through the Hog. Nothing will happen since you're not technically processing any TCP but nevertheless, it will put a stop to other devices interfering.

Also, make sure all your other devices are on a different subnet. Only the ArtNet out and Artnet In devices need to be on the same subnet. This way you can get away with an L2 switch that will work fine.