How does F5 PEM send API HTTP Requests to an orchestration system?
To answer both points - you are probably correct that this was a specific customised setup. As i'm sure you know, the flexibiliy of BIG-IP means that you can do most things in many different ways. We in Professional Services are often the ones to do those things so we have good experience of creating many and varied bespoke solutions depending on the customer requirements. As a general rule, it is not good to mix data plane and control plane ie to perform control plane scaling operations based on user plane data. A better way would be to create an iCall to regularly check video platform capacity and perform scaling operations.
Regarding VNFM, it comes with some standard Blueprints ie the network architecture required. This is normally a DAG layer and a Service layer - DAG is fastl4 loadbalancing over Layer 7 Service such as PEM, AWAF etc. This allows simple and scalable scalability. Service layer capacity can be measured using NAGIOS or suchlike, with triggers to scale up or down as required.
However, because VNF Manager is a fully featured orchestrator in its own right, you can create your own Blueprint or customise an existing one - so you could very easily scale the video platform, router, firewall or any other device which has an API. As with BIG-IP, it is very flexible and scalable so you can create a solution to fit your requirements precisely.