My advisees often have questions about the ethics of letters of recommendation (LOR).
First, some applicants tell me they feel guilty because - although they waived their right to see their LORs - their writers gave them their letters to read. If your letter writer crafts your LOR understanding that s/he has no obligation to let you read it yet chooses to offer you a copy, you have done nothing unethical. That decision is the letter writer's.
Furthermore, I've had applicants tell me they feel uncomfortable because faculty have told them to write their own recommendation letters after which the letter "writers" will edit and sign. Again, totally kosher. This topic was recently addressed here by the ethicist in the New York Times.
Remember to start early in asking faculty to write your recommendations. LORs almost always take longer than you think.