Universal uses the fingerscan for all multi-day tickets but not for one day tickets and not for annual passes. (Universal annual passes have your picture on them so there is no need for a fingerscan---sure hope they don't send my picture to the FBI as I do look rather scary in mine.)
It is not a fingerprint. They do not take a picture or inkblot of your fingerprint. It simply measures the distance of 5 points and stores that measurement. Let's just assume for a minute that all the records of those measurements are subpeoned by the FBI. What will they have? They will know that someone with ticket number 587256992723314972 has these 5 points on his fingerprint. They wil not have a picture of the fingerprint nor will they have the name of who used that ticket.
The system does not store a picture or data of the fingerprint. It stores a number. The finger print is scanned and some junctions are pinpointed that the program uses to generate a number. This number only is stored. Each time you put your finger on the pad, the unit scans to see if the number generated matches the one on file. The system does not store a picture or a electronic copy of the fingerprint. To store a simple multiple digit number that corresponds to the ticket only uses very little computer memory. Neither Disney nor Universal need or want to have to store the much larger information that a recording of a full fingerprint would require.
Disney has been switching to the one finger scan now also and the media has been making a big deal about it. I'd be more worried about getting a driver's license. For my last driver's license renewal, they got some pretty "private" information such as my full name, social security number, my home address, a photograph, and yes, even my thumb print. And that is from a government office. I am certainly not worried about a themepark having 5 measurements of points on my finger with no name or address attached to it.