Before you installed El Capitan did you install any driver for the UBC125XLT or did you just talk to it through a Terminal Control Program?
If you have tried using Scan125 then how exactly do you actually do this? e.g. do you boot Window 7 via Bootcamp, or using a VM, etc.
As I don't have MAC or any experience of using scanners on a mac, let alone my program then I'm very much limited on what aid/suggestions I can give.
If you installed a driver for Windows then there are TWO different drivers. The original BC125AT/UBC125XLT driver was very specific and in Windows the scanner would appear listed in Control Panel > Ports by its name.
There is a later Uniden Universal Serial driver and this one will just show as Uniden Serial Port (COMn).
If you are not using this later universal driver then you should try using it. Both drivers can be found here:
BC125AT < UnidenMan4 < TWiki