I always advise owners of chinchillas to keep the variety of their pet's diet to a bare minimum to minimize the risk of digestive upset which can sometimes lead to lethal complications.
It probably doesn't make me popular with people who like to give a lot of treats but I give my chinchilla only one kind of treat, very occasionally, and only at times when he has not been stressed. This ensures that delicate cycle of microbes and nutrients that occurs in his stomach and intestines is not altered.
I recommend raisins because they are proven to be safe by the industry, are inexpensive to obtain, and easy to chop up. Raisins or any kind of treat should only be given to a healthy, full grown chinchilla as training aids to facilitate interaction, and not as dietary supplements. Chinchillas get their full contingent of nutrition from their hay and a quality pelleted diet.