Since traffic over Omaha IX is exchanged based on BGP routes, there is no reason to answer ARP queries for any other IP address(es) than those that are configured on your exchange interface.
Unfortunately, some vendors (e.g. Cisco) ship their products with proxy ARP enabled by default.
Proxy ARP is not only sloppy, it can lead to unwanted traffic on your network. Consider that if you have it enabled at the AMS-IX, it’ll likely be enabled at other peering points, allowing parties on both sides to use you as a transit.
Proxy ARP is not allowed.