After attempting to install Hiero submitter I found that it was completely non-functioning:
The client script was not Py3 compatible, and replacing GetDeadlineCommand() and GetRepositoryPath() with those from the Nuke Submitter resolved those issues.
In the Main submitter, there is a an import for Pyside2.QtWidgets.QVariant on line 23 and line 27. I didn’t look too deep into this, but I think QVariant is obsolete.
This is only called on as a commented return type hint; so simply removing this import solved that problem.
I’m still getting occasional crashes on export from Nuke Studio; it will usually export and submit a few shots, and then hang indefinitely. I have not tracked down this issue yet, but it feels like maybe the submitter is somehow getting ahead of itself or something.