Am I correct in saying that Protractor must have the
Protractor/Selenium Webdriver installed on the machine where the tests
are being run but Angular Scenario runner executes within the browser?
If you are using NPM then you can have Protractor/Selenium Webdriver as local dependencies. They don't have to be installed globally. See https://github.com/angular/protractor.
I would essentially love to be able to run tests/scenarios remotely to
give potential interviewers an insight into the behaviour/nature of a
site I am developing.
Do you mean a live demo of the site using protractor or something like that to show the workflows and usecases? If so then you might be over engineering the solution. A Youtube video would have the same effect.
I have used iMacros in the past, however, the tests weren't strictly
portable between Firefox and Chrome?
Protractor tests are portable, you just need the correct webdrivers and make sure to point to the browser binaries.
Is my assumption about the difference between Protractor and Angular
Scenario runner correct?
I cannot answer this. I don't know enough about Angular Scenario Runner.
I would advise against it though as it is depreciated, see note at top of page https://docs.angularjs.org/guide/e2e-testing.