Well I imagine the business case (if they even send the same kind of notification to businesses, which I don't know to be true or false) is easy since presumably the business's name is on the account and said business has someone authorized to take care of such paperwork, and I doubt the letter would (or should, for that matter) be accepted if it comes from someone else in the business. Presumably Chase could call back the business's legal department and ask if they weren't sure if it's valid? Dunno, but I don't see it as a very realistic question.

In terms of you as a consumer using the template they gave you, I mean, in principle I would assume it would count (you put your signature on it and mailed it; it clearly signals your own volition and intent to opt out), but I could see a judge saying no if Chase gave a convincing counterarguments why (e.g. hypothetically if Chase had a habit of getting a lot of legitimately fake opt-outs that they couldn't distinguish from yours, and if it would be obviously bad public policy to accept them, then yours probably shouldn't be valid either). Ultimately I'm not claiming gray areas are nonexistent...