Yes I think all you need is to copy the method from the Pub > Controller > Forum > assertViewableForum method and use it in your callback and you can use it as the way you want it.
Thanks, but is it possible to directly use the XF > Pub > Controller > Forum ... function without the need of a custom callback? My plan is to use the existing xf functions as a php callback to display forum_list on a page using php callback.