Who do I think they're "selling" it to? I wouldn't say selling it, but more like being told to give it to the government, and being told to say nothing about it (just like my day job). It's my opinion, of course. Feel free to call it a tinfoil hat opinion, but it would not be an odd request.
In Canada, the only time a Canadian will usually be fingerprinted (or at least the only time in my life, and I'm 35--and I've had several jobs + college + accounts with every single major bank here) is when you go to jail. Some children are also optionally fingerprinted by the police in case they are lost (I believe those programs are deader than a doornail here now, because I've not heard of a peep to suggest my 4 yo be fingerprinted for one, they're also optional and the child may refuse. Optional as in just don't get suckered into it at the mall). I have heard that jobs at particularly secure sites require fingerprints (Nuclear reactors / CSIS).
Is fingerprinting common in the US? In Canada the only time it is routinely used is for criminals (or people who are arrested and thus likely to become criminals). Thus to those of us from here, the first thing we think of is government/prison when asked about fingerprints.
Anyways, as for how would a hash of the fingerprint be useful for the government? Investigation -> Pull Fingerprint -> Run fingerprint through algorithm Disney uses to generate hash -> Narrow search to a few dozen people -> Hassle the 3 or 4 likely suspects until you find the right one. I'm not interested in that hassle, no thanks!
BTW, after pressuring the email rep, I managed to get a reply that stated affirmatively Photo ID is an acceptable alternative. So I booked my holiday! Yay! Maybe I should wear gloves while at Disney!

Seriously, just joking!
Just read that and it sounds like I've been to jail! HA! Nothing of the sort, I assure you.