According to my gardening club magazine, which I just got today coincidentally, "tomatoes crack and split when fruit grows too quickly during a period of rapidly changing weather conditions, such as high temps and drought followed by a rainy spell." It goes on to advise that you, "Always maintain consistent irrigation during dry spells and mulch plants to conserve moisture. Or try crack-resistant cultivars such as "Bragger" or "Roma"." FINALLY, I get to answer somebody ELSES problem.
Yes, tomatoes will crack due to inconsistent moisture. Mulch will help this out a lot. Severe pruning can also cause this. Basically anything that will stress the plant out.
Like the other posts said, yes there are some hybrid varieties that are more resistant to cracking if watering is an issue.
THere are several type out the that are less apt to split under certain conditions. Some split easy other take a lot more. What kinds are you having problems with?