Please advise on whether user installed dependency wheels for addons is permitted

from a Gramps bug report with a proposed PR to resolve it:

The PR is not “allowing pip to modify a flatpak” — it is installing addon dependencies to user data, which is standard practice and explicitly permitted by Flathub.

In this app, add-ons (in this case these are app specific add-ons, not the Flathub use of the term add-on) can be installed with an add-on manager in the app’s toolbar. If an add-on dependency is missing, the add-on manager is supposed to pull in the extra dependencies with pip. Obviously pip does not work in the flatpak, which triggered the bug report. The PR in question will install wheels into a user data directory instead of using pip, as I understand. For my future reference, is this explicitly permitted by Flathub as claimed in the quote above?