From what I can see in a quick search (and from this presentation), Netflix only uses FreeBSD for serving video and they run these servers themselves in their own datacenters I guess. In contrast their apps on EC2 use Linux [0]. Sounds like the time has not yet come when AWS is paying anyone full time to support FreeBSD on EC2.
Netflix works because they move content close to the users. This is done by either having the ISP establish a peering connection directly to Netflix hosted servers or by having the ISPs host "Open Connect Appliances" which cache the most requested content. These appliances are based on FreeBSD.
The AWS egress savings from this setup must be immense.
It means, for example, writing a FreeBSD kernel driver for Elastic Network Adapter (ENA). Both Linux kernel driver and FreeBSD kernel driver is available at https://github.com/amzn/amzn-drivers
[0] https://twitter.com/brendangregg/status/1412201241472471048