So I have this sentence すべての会社は、才能ある人材を育成すべきだ. I'm focusing on 才能ある人材. I'm guessing that 才能ある is short for 才能がある. But then aru is followed by 人材 which is another noun. The translation is "people with talent". Does ある in this case act as an adjective to 人材 which means personnel to make the phrase "talented (or has talent) (才能がある) personnel (人材)" or "people with talent"?
Here ある is modifying 人材 as a relative clause. A very literal translation of 才能(が)ある人材 is "human resource where talent exists".
ある is not the only verb that "works like an adjective". Actually, if you look at the grammar of Japanese relative clauses, you may notice that all Japanese verbs can act like an adjective! I don't want to confuse you, but this is why some linguists argue that Japanese actually has no distinction between verbs and i-adjectives. In fact, verbs and i-adjectives conjugate a bit differently, but functionally speaking, they are surprisingly similar.