Sous Vide danger zone for vegetables
The issue with the "danger zone" has to do with bacteria that are on the food. There are 2 issues. 


fresh food may have harmful bacteria on it. This is more likely by meat, but vegetables can have them too (this is why you wash off that apple before you eat it) Getting up to 140 degrees kills off everything. 
any bacteria that there is on it or lands on it post cooking. If the food is kept warm but under 140 or ie;danger zone then these bacteria have a wonderful place to live and can quickly grow. This makes no difference between animal or vegetables.