Early versions of the UBass had a passive pickup and no integrated tuner. My first model was like this and I had a hard time getting a tuner that worked.
When I first got my UBass, I found tuning could be a little tricky. I discovered that not all tuners would repsond to plucking a string on the UBass, indeed my in-line tuner (connected by cables) tended not to pickup the signal level even with the active pickup on a SUB Ubass. I don't really know why this is but I had to try a few different tuners before I happened upon my favourite. When I'm playing on stage I use a Qwik Tune Snark Clip On Tuner on the headstock. This responds to the plucking much better than others I tried. There is still problems in noisy rooms but that is unavoidable.
The other one I have successfully used is the on-board tuner on my Roland Micro Cube BASS RX Bass Guitar Amplifier portable amp. This takes the direct signal and allows you to tune strings even in noisy situations where the clip on tuner fails.
Even with these pieces of technology I find tuning a pain in the ass. The polyurethane strings seem very susceptible to temperature changes especially in winter where strings can be quite hard when you taken out of the case and take a while to warm up. This means in the first 15 to 20 minutes you get wild changes in tuning. So in any playing situation I tend to leave my base open to the air as soon as I can, in order to let it acclimatise. Luckily when temperate is stable and the tuning is done, the UBass seems pretty reliable at holding it's pitch.