b) Each forum will probably have it's own upload system but it will be the same or very similar from an iPad. There's often a "choose photo" option which would be fine, the issue you may have is if there's only a "drag photo to here" option.
Check on your iPad - many sites now display a slightly different version for mobile devices so what you see as the "drag…" option on a Mac may display as a "choose…" option on iOS.
If all else fails, contact the forum owner for an update. I believe tablet devices are now quite popular ;-)