The strings shouldn't break as long as you use the appropriate guages (thicknesses). At least, they shouldn't be any more likely to break than "normal" guage strings in "normal" tuning, nor than the upper-register stings in each pair of strings on a 12-string guitar (which is what the Nashville-tuned strings essentially are).

Re-read the above for several different opinions about the exact guages to use, and also (I believe) there is a reference to one string manufacturer/vendor who markets a six-string set specifically designed for Nashville tuning.