I've used my UA-5 to transfer DATs to my computer without any problem. There definitely is a redundant resample step if you're transferring a 44.1 DAT to a 44.1 WAV file, but if you have a DAT sampled at 48 and need a WAV at 44.1 to burn to CD anyway, then the resample step is necessary somewhere anyway, and I doubt it makes much difference whether it is done in the UA-5 or in SF or Audition or whatever software you have. Even 44.1 DATs, the redundant resample is sonically transparent.
I wouldn't recommend BUYING a UA-5 for this purpose since you can get a bit perfect soundcard that is cheaper and technically superior, but if you have one and don't have a bit perfect soundcard already and don't feel like spending $100 or whatever to get one, I see no harm in using the UA-5 to transfer your DATs.
Also, FYI, I run the DAT into the coax input on the back of the UA-5, then connect to my computer via USB (and make sure the sample rate dial on the front of the UA-5 is set to 44.1 regardless of the sample rate of the DAT). On my computer, I use Soundforge 8. There is an audio capture feature in SF. You just have to select UA-5 as the input device and you can record to wave (SF should automatically detect the UA-5 when you plug in the USB cable, if not, read the book on how to install the software). Also, and this is important, don't use the computer while you're doing the transfer. The computer (NOT the UA-5) will drop samples and give you subsecond skips in your WAVs if you're using the processor to do other things while you're doing the transfer.