Answer: Usually not
Rennet is an acid produced, mainly, in the stomachs of mammals. Rennet helps young mammals break down the milk produced by their mothers. It is primarily used in cheese production to separate curds and whey. It should be noted that there are a few vegetarian friendly sources of rennet. They will often be noted as being from vegetable or microbial sources. I have personally never seen rennet used in ANY vegan product or dish.