I have never understood the allure of using your iphone as a hotspot for your ipad.
To me, the allure of the ipad (and iphone, to some extent) is its always on feature. I have the urge to find something out, or have a few minutes to burn, just whip out my ipad, flip open the smart cover and start surfing away.
With the above alternative, I have to go through the hassle of toggling the hotspot option on and off as need be, and still have my ipad connect. Not to mention that it likely burns through your batt power very quickly, and I will want my phone to last all day exactly so I can take calls/messages. Sounds like quick surfing would be a real chore.
Not saying it cannot be done, but just like with trying to type an essay on page in your iphone, it doesn't sound really feasible or practical at all?