Hi Crow,
You could certain edit a hosted feature layer from AGOL in ArcGIS Pro. You are correct, you would access that data through the Portal tab in the Catalog pane. The data would need to be editable obviously.
The issue you may run into is that the data would act the same was as editing non-versioned data in a file geodatabase (or anywhere else). The last person to save edits wins. In other words, the last person to save their edits will overwrite anything that is done by anyone else beforehand. There is no structure to separate out edits or look for edit conflicts. It is the same way it works in Desktop now for you guys.
There is no issue with downloading data from AGOL, modifying it, and republishing it. It is a perfectly valid workflow. Others may choose to keep the local copy of the data be the authoritative copy of the data and then upload it to AGOL when they want to update the data there. But both are perfectly fine.
Let me know if you have any further questions.
Jonathan