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Not certainly.
The section on Ray spells state that they are aimed as if using a ranged weapon, meaning they use the aforementioned rules, but not that they are an actual weapon.
For instance they cannot be disarmed or sundered, as they are not actual weapons being used. And that seems to be the gist of the Blackened curse effect, as you take a penalty to weapon attack roles and the reason why (descriptive text) is that your hands are burned and sensitive to the touch.
Considering Paizo doesn't generally FAQ or Errata any splat books as they are not reprinted, expect this one to be open to interpretation. Also consider that the cus grants a ray spell as a bonus, which would seem pretty crappy if the intent were to penalize it.