I might clarify a few elements for you.

The parallel command I'm using is not JLink specific. It's akin to ParallelSubmit, as I mentioned, in that it submits parallel evaluations without automatically waiting for their execution. I'm using it in preference to ParallelSubmit in this example as it removes the queue interactions that would obfuscate the core issue. I'm using it in my target use case as I require traditional ParallelSubmit functionality on a subset of my parallel cores, and simultaneous controlled parallel execution for this purpose. A similar situation is seen in this stackexchange question. I am thus under the impression that your primary suggestion, to run in parallel directly from the front end, is what the code I posted already does. I do not understand how I would invoke a second front end from the parallel kernel as you mention. I would further be concerned with the undesired side effects (i.e. a literal second front end) of doing so.

I am indeed using the Java interface to create OS side effects. In my constructed example this involves mouse movement. Whilst I suspect diagnostically this is using the Mathematica front end, at a high level I do not see that this use of the front end is a conceptual necessity. As to if the front end is a literal necessity in implementation, and if this can be either achieved or subverted, is the core of my original question.

Your expectations on the causality of the waiting of the front end do not hold under experimentation. I have omitted a large suite of diagnostic experiments I have performed to try and convey the issue as directly as possible. It's a valid hypothesis that the front end is explicitly waiting for the Receive output, causing the connection, but this is not the case.

You mention that JLink may be inherently connected to the front end. This aligns with my suspicion that behaviour differences between JLink executions on the front end slaved master kernel and the parallel kernels are caused by a lack of a direct front end connection. I would like to both explicitly confirm this hypothesis, and understand its consequences. You mention JLink code for disconnecting from the front end. Would you be able to come up with any examples I could try, or specific documentation?

I am unconcerned with losing Mathematica view of the mouse.