You cannot render to clip-based formats this way - not ever. This has nothing to do with AE or Media Encoder, this is a simple thing with standard operating systems not supporting concurrent write operations to the same file. A file always gets locked by the first process that writes to it. It doesn't matter where and wehn, that's just how it is. Anything beyond that would require specialized server operating systems. Of course even that's assuming there was actually a built-in way of keeping the linear logic of the clip and the prerequisites were present in Adobe products, which they are not. So like it or not, you have to restructure your workflow and server farm to accommodate the demands or even buy yet another computer just for the encoding. The rest we cannot know. Any comp can render forever if only it has enough crazy stuff in it just like fancy features that require multiple temporal sampling will nullify any advantages multi-machine rendering may have since every machine needs to calculate extra frames to e.g. get correct results of a CC Force Motionblur or Echo effect. Conversely, all your pre-rendered stuff could be meaningless in such a scenario, since AE would duplicate your files to create temp files and/ or take forever to decode long clips to just access the current frame. The network traffic alone could kill it. You'd have to be much more specific before anyone can tell you whether or not there would be any advantages. In any case, I think you have some thinking to do...
Sadly, yes Mylenium's answer is most correct, in my experience AE's multi machine rendering has come in great use with projects originating and ending inside AE though. You Render and Img Sequence on >1 computer and then one computer needs to take the Img Sequence, add Audio, and render that to a single movie file.
Now the next sad part, concerning the 40 windows machines you have access to. Apple's Compressor has been known to do some "Distribution rendering however it only works for Mac OS Machines. I would explore the options that Compressor has. It's the only encoder that does anything close to taking one video file, chopping it up, distributing it to other machines for encode, and then marrying them all back together. Do understand that it's always been a bit finicky and I have never had the opportunity to give it enough.
Which leaves me to a new thought - AE Media Encoder Watch folders - so you get X number of videos, say that number is 20. Make 5 folders on your shared Media storage and Manually (or using a program like Automator on your mac) distribute those 20 videos among the 5 folders (4 videos each) - AE Media Encoder on each machine doing the rendering is watching 1 folder each and so all of a sudden, 5 machines start processing through 4 videos. It's more manual but MUCH less wait time.
Also There can be other automated processes to help move your files into their respective folders - look for ways to use Automator (comes installed with all Macs) and/or Hazel by NoodleSoft. Both have watch folder features that apply any number of custom workflows to the files.
I have Hazel watching over my entire project directory and when I render out a ProRes422 MOV with the "- 1080.mov" in the name, she knows to pick it up and copy that MOV into a folder. A dummy "Render" user logged-in in the background has Media Encoder opened and will immediately start encoding the files that get dropped into that folder.
Multi-machine render for IMG Seq from AE –––> Flattened into a single MOV –––> (This is where stuff gets automatic and now can apply to your workflow) Hazel picks up the file and copies it to a folder –––> Media Encoder sees files and Encodes for Delivery to client.