Thanks, I totally agree with you and would prefer to just use Hyper-V and be done with it but my boss had some security concerns and wanted an evaluation. suffice to say it won't cover this specific application.Answering because I do a bit of real-time programming in my day job...
@leesteken is correct. Nothing is actually real-time in a VM since it is just another Linux process. The only real-time in that context is with respect to the VM's clock, which may have arbitrary amounts of jitter with reference to the outside world. It might work for development purposes but I would not rely on real-time in a VM for anything production, at least not without doing a lot of characterization. There are trade-offs that depend a lot on the application requirements.
For example, at my job I've been working with some customers that would like to do this very thing for a fairly complex signal-processing application. The answer we are converging on is to re-architect the solution to change the hard real-time deadlines into throughput requirements + much looser deadlines that un-patched Linux can meet. Then we live with the extra latency that will cause. For a lot of multimedia-type things (speaking very broadly) that approach will work, but not necessarily for other things.
@j.tagscherer I don't know that you can make Proxmox look enough like Hyper-V to make their software work. I think you'd need to know a lot of details about what the vendor's requirements are and work from there. A quick glance at the web site makes it look like the SW isn't hard real-time but probably does need specific behaviors from the serial port or something like that. That said, if this is for a deliverable product not following the vendor's recommendation would be a bad plan IMO.