I am not aware of any such restriction.
On the contrary, I implemented a Forge room editor app that communicates with a Revit add-in:
https://github.com/jeremytammik/roomedit3d
On second thoughts, that does the opposite of what you are asking for.
Still, there is no reason that you cannot call a Forge app from a Revit add-in, or any other web app, for that matter.