I do keep the seeds moist, but I really monitor the moisture levels to make sure the soil does not get too moist. My hypothesis is that these seeds would probably rot very easily. A second seed just started germinating earlier today, so I must be doing something right. Or, I have gotten some germination through blind luck. Probably the latter.
If you get any of your seeds to germinate, you should probably keep Ziziphus joazeiro strictly as a container plant. South Florida soils probably do not drain well enough to prevent root rot for this species. Assuming I can keep my seedlings alive, when I transplant them into larger pots, I am going to use some sand to create a very well-draining soil mixture and avoid the urge to overwater them. I am also going to use clay pots, not plastic.