Whether to run the DAS on a different host that the instances depends on
the characteristics of your production environment. For example, it may
be desirable to prevent all outside access to the DAS by running it on a
separate administrative network. With this arrangement, you have a
multi-tiered network, with a load balancer tier, an instance tier, and a
DAS tier.
Another reason to run the DAS on a separate host is so that it's
processing doesn't interfere with the resources that are available to
instances.
If these are not concerns for your environment, then the DAS can be run
on one of the instance hosts.
Tom