LAPD has along tradition of letting officers moonlight. Remember, they are sworn peace officers 24/7, while at work, or mowing their lawn. This moonlighting dates back to the days when LEO's were poorly paid, not like today, where the police union own the City, and are happy to drive it into bankrupcy.
They have done private security gigs at certain nightclubs for as far back as I can remember. Some retired LAPD officers wear their full uniforms and (slightly smaller) retirement badges and have police style duplicate motorcycles and provide security for movie and television for many productions every day around the Los Angeles area, keeping back people they don't want around. Several active officers control this service, and they do not limit it to just the LA city limits.