Java version on forwarder machine

I know it is highly recommended to use Java 8 for elasticsearch and logstash. Is it highly recommended on machines running just the logstash-forwarder also?

logstash-forwarder is written in Go and isn't dependent on any JVM.

Or are you conflating the logstash-forwarder program with Logstash proper acting as a forwarder? In the latter case you should be fine with Java 7.