Will becoming a security guard hurt your future rap career?
Probably not, there aren't any restrictions for previous jobs if you'd want to be a rapper. The most important criteria is how good a rapper you are and what the market is buying.
No. Securitas and other large security companies do not require these degrees for security guards. You only need the degree if you are looking to become a licensed peace officer. You may obtain this license without becoming a police officer and it will advance your career in a private security firm if you become licensed.