Oh absolutely not, I don’t host any of my work dependencies on hex.pm, it would make no sense. They can either be git or path dependencies (I use git as I have a little hosted git server at work) or other options as well. 
I find them quite significantly more difficult to work with overall. They encourage touching code across sections that should be touching code (this is why the dependency graph makes things wonderfully explicit and clear), it’s more code to go through at once (easier to ignore little things when there is just sooooo much to deal with, compared to nice fully compartmentalized libraries), it’s easier to PR in to and have the CI run tests on it, etc… etc… Mono-repos are an absolute horror after having to deal with far too many at my old jobs at such ‘big corporate’ places, the amount of time changing something innocuous and private breaking ‘others’ stuff was utterly astounding! o.O
