The frequency of ARSs in natural DNA was about what was expected based on the spacing of oris detected microscopically. It was clear that ARSs work as origins in artificial plasmids of yeast. A great deal of work, which we don't have time to go into, has investigated this question. The bottom line is that, yes, at least in general, yeast sequences that act as ARSs are bone fide origins. That is, when in their normal chromosomal site, they can serve as origins of replication.
Replication starts at ARSs.
Curiously, it has been found that not all origins are used each cell cycle. Potential origins are spaced roughly every 30 kb but not each one is always used.