Telling VRS to connect to modesmixer on port 30005 should be enough providing you are feeding mlat results to it. I don’t know if it forwards the mlat indicator on that port though, so you may not be able to tell the difference in VRS.
The way I have it set up is to have two receivers in VRS - one for the mlat client and one for dump1090 and connect to them directly. The mlat client is set to listen on port 30105. I then created a merged feed from both receivers which displays all the data together.