I have a setup with a load balancer in front of multiple Portals and multiple Server sites with clustered machines. Is it possible to use the VSP Engine Tools POST installer for such setups and what would I have to consider?

Yes it is possible to install the VSP Engine Tools in this scenario. You will need to install the VSP Engine Tools to one or more portals behind the load balancer. The tools are installed on each server machine clustered to the server site selected during the installation (VSP 5.24.1 and higher) or on the first available hosting server site (VSP 5.23).