No, Green Spot Algae is not harmful towards fish.
However, I do recommend getting rid of it. To get rid of green spot Algae, limit your lighting hours by half and keep dosing your fertilizers if you're using any. Also, you could dose some Seachem excel for once a week and see if that works
Reducing the lighting hours only decreases the growth of the Algae in the tank, it does not stop it.
Green Spot Algae appears when there is a lack of phosphate in the aquarium. So, As I stated above try using Seachem Excel. If you use the proper dosage per week the Algae should be gone. Also, since Green Spot Algae enjoys light reduce your lighting hours to decrease the growth of it.