Hi @RockStarArtist,
First we have to distinguish two things here, Fast DDS Discovery Server and DDS Router, as they have very different purposes.
The first one, Fast DDS Discovery Server allows you to change the default mechanism of entity discovery based on multicast discovery to a client-server architecture based on unicast discovery.
So yes, all multicast traffic is removed with the Discovery Server.
In addition, the latest released version of the Discovery Server allows you to reduce up to 93% of the discovery traffic by discovering only Publishers and Subscribers that belong to the same topic. Here is a link to another post in this forum where we presented these results.
On the other hand you have the DDS Router whose purpose is to connect DDS networks in a simple way and with a very basic configuration. In this case, the DDS Router will not interfere in your local or isolated DDS network, since the only thing it will do is to relay the data from one DDS network to another. What it enables is to decide which topics it will forward in order to avoid unnecessary or redundant information from one network to another (allowlist/blocklist feature). Here is an example of how to configure it to connect two DDS networks and another example of how to perform a DDS Domain change within the same network.
I hope this clears up your doubts.
Cheers.