No experience with the U-HID, but I'll give it a try...
Do the axis for the throttle and brake work when you check it under Game Controllers in the control panel?
Do they show up as separate axis, or two halve of the same axis?
Model 2 requires them to be separate. The games you mentioned also require them to be inverted in the Model 2 input menu.
(I think both pedals need to be inverted, but it might just be the gas. They are all the same way except for the two Jaleco games.)
In MAME, it could be that the joystick needs to be enabled in the ini file.
See the MAME section of the driving cab thread about joystick deadzone and saturation.
Driving games suck bigtime with them set at the defaults.
Running MAME 102, but can easily upgade to 141 if needed.
You're probably only missing out the Cruisin' series with that build.
It takes a fairly fast processor to run them though (2.8Ghz dual core in my experience)
The cool thing about the U-HID is that it can handle input from both a potentiometer and an optical encoder.
So if you had a wheel that spun 360 degrees and a continuous rotation pot, you could have both the 360 & 270 degree wheel games covered.
If it had outputs for a FFB motor, it would be a perfect interface.