Commtouch engine is also used for some kind of URL filtering - is the http proxy enabled and content filtering active? This would explain the DNS requests.
Since reputation and categorization lookups must happen very quickly, the systems can be a little "chatty". They are checking frequently to make sure the system has the latest server information at all times so that lookups will be as close to instant as possible when they are done. As with any distributed system, individual nodes may come online or go offline for a variety of reasons, thus the frequent checking in.