Horizon Cloud Service does not include an antivirus solution. You can use the solution that you already have by obtaining additional licenses for the Horizon Cloud Service environment. However, this is not a Horizon Cloud Service requirement.
If you choose to use an antivirus solution on your Horizon Cloud Service desktops or RDSH servers that updates DAT files, it is best to stagger the updates across your environment. Doing so protects you from using all the resources in your environment to update all your VMs at the same time, which could result in slower performance.
In addition to staggering antivirus updates, it is best to use a fixed schedule that avoids large concurrent updates, such as updating outside of normal business hours or creating a maintenance window. Avoiding large concurrent updates also prevents using all resources at the same time, which can slow performance.