It depends on the uke I guess. It's my understanding that the best steel string electric ukes are made by Risa, who also makes two other models of passive-pickup nylon string electric-only ukes.
Then there's the very popular Bugsgear Eleuke, which I believe has an active pickup and the pictures clearly show tone and volume controls.
There's a new one made by Koolau, and then there's the Pete Howlett Uklectic.
Of all those, I've had the Risa uke-solid concert, which had an almost-too-easy-to-drive pickup but otherwise no complaints about it. I've played the the Eleuke, but I just didn't find it much to cheer for.. probably because I was sitting opposite the guy who built the Uklectic I was just about to buy.
I say the Uklectic is beyond great, but much depends on the quality of the pickup. Mine is right down the middle. Another UU member has one that favors the mids and lows too much once it's plugged in. And of course what you plug it into, like the quality of your amp and/or preamp, and the cables you use, and the headphones you use if you're using those - they all play a role no matter what instrument you're plugging in. Any piece of gear has its own coloring to the sound.
But if you're just talking about acoustic ukes with pickups installed, then the ukes function as normal ukes. Just plug them in if you want to amplify the sound or play with the original sound.
The Risa didn't have the sustain that an acoustic uke has, but you could make it do whatever you want. The Uklectic is worlds easier to play, has that traditional sustain, and as it is with electric instruments, it'll do whatever you want. You're only limited by what you plug into.