I get a VDC/ABS/SLIP light combo whenever I disconnect the battery on my Nissan's. It requires an ABS reset. For mine at least - you can either drive for like a couple hundred miles and they will eventually reset, or do a manual reset by getting the car going perfectly straight - shut the engine off - restart the car and drive forward to 16mph without touching the steering wheel. The steering wheel can't move at all - hence you need a nice flat empty parking lot or similar. Somehow it re-calibrates the speed sensors.
Wheel speed sensor codes would be Cxxxx code - I don't remember which but I would expect to see that code if it was a speed sensor issue.
The U code is a high level code between modules, however Nissan's are strange about firing U-codes when you have other issues. I have never been able to find anyone that can explain why, and half the time the U codes aren't in the service manual, but you will usually still get a more specific code you would expect to see along with it, at least based on most of what I see on the Nissan boards.
As for reading the ABS codes, that's another issue in that a lot of scanners won't read Nissan codes outside the standard engine codes, or need a software update specific to Nissan. I have read the FOXWELL NT630 works for Nissan ABS codes, but I haven't bought one so I can't confirm. If I ever find one I know for sure will work I will buy it.