A shoulder subluxation is a minor dislocation of any given joint. This can only be truely confirmed with a hands on assessment. Regardless, if the joint is damaged or lax there may be underlying structures that are damaged, but because you did not state any trauma I doubt that it is a True subluxation. Most people by the virtue of decreased activity probably have some degree of instability around the shoulder joint (or pseudo-subluxation) regardless.

I do not believe constant Wikipedia reference-linkRotator Cuff work will solve the problem. There are simply too many muscles surrounding the shoulder to place the emphasis on just these muscles. There are joints, ligaments, and muscles attached all over the humerus and scapula. Obviously without having seen your workout form, and assessed in your arm in person it would be difficult to tell which muscles are over-active and which are under-active. Which muscles are short, and which have lengthened.

I suggest you proceed with caution, begin by finding a range of motion with bench press that is comfortable for you. Additionally if you choose to continue with rotator cuff exercise, I suggest you get a qualified professional to guide you through them. Depending on the position of your arm you will target different muscles.

Regards