Yes, I thought you knew this - I've always hotspotted with UNPDA and the native Personal Hotspot functionality on the iPhone which explicitly uses inet.bell.ca. Others (search around the forum) have also not been charged for using that APN. The hotspot usage shows separately (under "internet" instead of "mobile browser") but it shows as being included. If it were not allowed Bell could simply flip the switch and disable Personal Hotspot on UNPDA accounts--or, if they're feeling particularly evil, charge separately for it.
It's a good thing it worked too, because the "profiles" people teach you to install on the iPhone to enable tethering do squat - the only way to change it is to jailbreak.