I am not an expert at all for VMWare Horizon View and it has been a while since I worked with it.
Are you using the default script? For DNS servers, domain controllers, Global Catalog servers, mail servers and web servers, Veeam Backup & Replication uses a script that probes an application-specific port and I believe that is port 80 by default for webservers (I can be wrong here though...). If I remember correctly, port 80 is not open on a Horizon View Connection Server (can you test manually on the running server?)
You should be able to find the script XML file here: %Program Files%\Veeam\Backup and Replication\Backup\SbRoles. Inside the script for a web server role, you should be able to see what port we are testing
Hope it helps