Currently Greenbone uses the GMP Scanner type for master-sensor setups. This requires the gvmd on the sensor machines. It works well and we have customer setups with quite a number of sensor units controlled by a single master. We have added a mutual trust control/management into Greenbone OS to prevent MitM.
I assume with some fiddling you find out a way to run multiple openvassd via OTP. I never tried it myself and OTP is a dead-end technology anyway: We are already working on the next generation where we use OSP for controlling OpenVAS sensors. One of the major changes is to get rid of OTP: