I can't use the finger scanner either; I have advanced arthritis in my hands and my fingers are permanently "clawed" in a position that won't accommodate the flat scan surface. It's never been an issue. I go through the entrance queue in my
scooter and 9 times out of 10 I'm not even asked to use the scanner. If I am, I just explain the problem and it's not a big deal.
Disney's policy, I believe, is that park tickets can be swapped within a family group. For instance if a group visits the parks with two parents, six kids, grandparents and maybe an aunt or sister-in-law thrown into the mix, it isn't necessary to keep track of which physical ticket belongs to which specific person. At least that's how it's worked in the past. I only visit WDW once a year and haven't been since last summer so I'm not sure if the policy changed when the new RFID wrist thingers were announced.