Yes, chinchillas can eat rose petals as long as they are dry.
Chinchillas do not do well with eating wet foods and therefore it is important that the rose petals are fresh and dry.
If they were to eat wet petals then it will possibly cause digestive problems with your chinchilla and therefore is best to be avoided. It could also make them sick.
Therefore just feed your chinchilla fresh dry rose petals once in awhile as a treat and they should be fine.