How on earth shall I design the ground planes for mixed signal circuits, split or not?
Splitting planes 'as a matter of policy' is almost always bad. It means the people advocating it can't think their way through what needs to be done, so fall back on rules of thumb. Zero ohm resistors connecting regions may be useful to save the perpetrator's faces when in last-minute hacking to reduce problems, these links are randomly connected and removed until hopefully the circuit scrapes into spec.

Just because you write '0v' on a circuit diagram doesn't mean it's ground.

Trace the signal currents 'out' through the circuit, and expect the ground current to return on the ground layer parallel to the signal path (this is Maxim's path of least AC impedance). If it can't, because of a cut across the ground plane (I hate those ground flood fills, that then later get cut into lace-curtains by added signal tracks), then you have a problem. I like to route my grounds, as traces, parallel to my signals. Soon, those traces will start to form loops. Each time a loop forms, that's a good point to evaluate just what current path through what ground impedance may be presenting a small voltage to somewhere else. If you have a problem with these ground paths, then you change your floor plan now to untangle them. It's easier to do it piecemeal at this stage, than route the whole board and then try to untangle it. Eventually, the whole ground gets filled anyway. 

If a high current curcuit dumps current into one end of a trace, any other circuit sharing that trace will see some of the stray voltage developed across it.

That Maxim link is one of the clearest guides I have read for what to do. However, be warned, it is very difficult to keep your head and apply it, with a lot of ICs on the board, and some expensive consultants snapping at your heels and wining and dining your boss to win him over. Remember, professional means they take money for what they do, it doesn't unfortunately mean they understand what they are trying to do. Good luck.