Like I said earlier, multi billion dollar corps cover their bases. Even if a cleck approves a warranty replacement and authorizes you be sent a new or CLNR phone, when you return your phone, your phone will be checked and if the tech finds that your phone was previouly rooted, the warranty replacement will be denied and you will be notified of the decision. You will also be informed that your account will be assesed the full retail price of the phone you rec'd.
Again, multi-billion dollar corporations cover their bases. That's why they are multi-billion dollar corporations and not just a "mom & pop" corner store.
Of course, there's always a chance that a few will slip through the cracks. So if you're a gambling man, go for it!