I agree with Jude. Better to be safe - you don't want them charging your account full price for a new Incredible if they discover that it has been rooted.
Is it being returned for warranty or insurance? If insurance, one could just claim it lost then keep to use as ipod touch. Not exactly the best way, but it would work...
I've heard of people with the OG Droid getting charged for sending back rooted phones for replacement. I tend to try and, pardon the pun, root out the hacked phones, and reflash them.
Having the tools to fix these things helps bigtime, sometimes even causes very curious co-workers with Droids..