[DeathTBO]

Yes it is still necessary. You won't be able to connect to the server without it. You will get an error "Unable to locate game session".

I'm part of a Dota 2 classic group and we were looking for ways to get Source 2 dedicated servers working, and this is our current roadblock. We usually play 6.84 (which is available on Source 1 and Source 2 engines) from 2015. Source 1 dedicated servers work.