I'm a nobody here on the forum but I'll give my two cents and maybe someone can correct me to help you out...
I use Octoprint with several Ender 3 Pro's and Taz6 machines.
The short answer is, your question seems incomplete which is probably why nobody is replying...
Your Ender 6 printer is physically connected to your Raspberry Pi (right?)... but without any software on your Raspberry Pi to communicate with your printer (such as OctoPrint), there would be nothing for Simplify3D to communicate with on your Pi (even if it could)? What software on the Pi is communicating with Port 3000 and your printer?
Perhaps you can expand how do you envision this working? What's the "use case?" ie... Simplify3D connects to what software on your Pi? And talks to what software on IP port 3000?
Given how robust OctoPrint has become, I'd say just stick with OctoPrint...
The best case is that Simplify3D implements a communication mechanism with OctoPrint and then you can connect to your Pi. (As "all" the other slicers do)
Hope that helps or spurs on some thought and I apologize in advance if I've missed the point...
so if you just use a USB cable and connect your pc to the printer directly, you can then control your printer thru S3D and without the middle man (Pi).
As you describe your question, you are in essence making the Pi a pass-thru or router/switch.
Kinda of reminds me the other week after installing the silent board on the Ender 5 Plus and then after confirming it works by homing only, I never started a print, I then setup the Sonic Pad to control the printer. Nice $$$ spent on those quiet drivers but the rest of the board isn't being used for the most part now. Kinda wondered if I didn't waste my cash on that board now but hey it was plug n play.
CR-10S "Trailer Maker"
CR-10S "Black Betty"
Ender 5 Pro "Ginger"
Ender 5 Plus "Wilson"
You can use postprocess script to upload to octoprint, you can install wget and create script for it or you can use gcodestat to do that for you.
In the github page of gcodestat: https://github.com/arhi/gcodestat you have explanation how to set it to upload file directly to octoprint when saving it.
gcodestat integrates with Simplify3D and allow you to
Calculate print time accurately (acceleration, max speed, junction deviation all taken into consideration)
Embed M117 codes into G-Code
Upload your G-Code directly to Octoprint
open source and unlicence