OK to nail into roof flashing?
Roof flashing along the place where the roof joins the side wall is designed to keep water from leaking into the underlying roof and wall. You do not want to be nailing, stapling or drilling holes in the flashing because it invites many leaks to start.

Find another way to run your cables. Inside under the roof, under the eves of the roof overhang etc. This will be a good thing too. The coax cable jackets will be much better off if they can be largely shielded from the sun.