Hub allows you to import attachments together with assets, at the same time.
To do so, you will have to use the Cloud Import JSON method for importing assets, as explained below:
In your project, go to the Assets tab and click on the Add Data button.
From the dialog that appears, enter the Upload Data URL tab.
Prepare a JSON formatted like the following. It is an array of objects, with each object representing an asset. Each object, then, in its attachments property, will have a list of attachments, like so: