Yes, of course. You can have all the same plugins or all different ones, obviously.
You can configure your SMTP host with the same SMTP information (if your provider has the capability) or separately. I use the same SMTP host when I set up in this manner, but we don’t have much traffic because I disable digests; but this is a totally different (unrelated issue), how to set up SMTP mail.
Regarding “what you call it” … well when we set up 20 LAMP apps on a server, we do not call that “parallel hosting”, so I do not think the name is important. You can call it what ever you like!
The point is that, it is easy to set up and works flawlessly.
Others are welcome to make things as complicated as they like. As mentioned, I am a KISS sys admin, and I like thing simple, easy to setup, and replicate fun and reliable. If you love complexity, do not follow this method, as it is too simple 
and does not require a lot of discussion but it works flawlessly and with other web apps on the same proxy, no problemo!
As a site note, I think many people want to run multiple discourse sites on the same server, in a manner similar to this. Running many discourse sites as virtual hosts behind a reverse proxy is the same as running any web app behind a reverse proxy. Personally, I prefer to keep thinks simple (KISS) as mentioned.
All the best and stay creative!
