Bob knows a lot more about O scale locos than I do. But I have a 2nd generation Weaver GP38 that has U-joints. Strictly speaking it's not a tank drive, because the high-low transfer tower is mounted on one of the trucks. But it does have an underfloor drive shaft that runs the length of the body through the fuel tank, with two intermediate U-joints. It's a 3-rail unit. I've operated it through un-eased "O42" (21" radius) circular curves with no issues. The driveline angles get pretty extreme, but it works without hesitation or binding.
The U-joints used by Weaver / P&D have a telescoping yoke. I like this design better than the slotted hollow tubes originally used by All-Nation, etc. Without some kind of telescoping shaft and a provision to retain the horned ball / swivel, I can definitely see the ball sliding out of the cup on a sharp curve. [Now let the debate begin about whether the slots on opposite ends of the tube should be in the same plane, or offset 90 degrees! 
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Sunset 3rd Rail has recently offered F3s and GP7s which are a central tank drive with U-joints. The 3-rail versions are rated to negotiate un-eased O54 (27" radius) curves. With a telescoping shaft or sliding yoke the geometry can be made to work. But I would agree that a truck-mounted system is probably a better choice for very sharp curves.
