Can you eat them? Yes, if the split is small and superficial and you pick and eat it right away, like in the cherry tomato above, it should be fine. Some larger tomatoes split, too, and you can cut out the crack after washing and eat the good parts. If cherry tomatoes have been split for a few days, however, you may want to toss them in the compost because mold and rot may set in.
Split tomatoes occur when the water available is inconsistent, like when they are allowed to get very dry and then watered. They can also get split after a big rainstorm. It's not really a big issue if you pick and use them right away. But to keep them from splitting make sure to keep the soil consistently moist (but not soggy).
You can also grow these 10 Heat-Tolerant Tomato Varieties
that are less likely to crack during hot dry spells, but don't let them dry out too much because most tomatoes will split if allowed to dry out to much and then are overwatered.