No, they're not. Rockers only increase the amount of lift, but keep the stock duration and valve timing. A cam changes valve lift, valve duration, and valve timing. The last two are most responsible for the exhaust sound of the three.
I'm with Bio. No need for a cam if you're not looking for really low times. Rockers with the right springs can provide the needed top end without the extra stress on the valve train a cam and tougher springs will put. Personally, while cam'd cars sound cool at the track, I don't want to drive around all day listening to that at every stop light.