Spalting softens the wood, not a bad thing when a cooks main concern is keeping knives sharp. If serrated knives are used on the board for things like slicing bread, they can eat up a softer cutting board fairly quickly. A grain or two of sawdust isn't going to cause health concerns as long as the cook knows and follows food safety rules. Microbial contamination is a much greater concern, at the extreme, causing death. As a cook, I prefer edge grain maple. The fancy cutting boards will go on display and not get used. A working wood cutting board should be washed with bleach water every day.