Yes, but if there is V Fib, the AED would help. More important and useful for chasers would be a CPR mask and training.. The heart will often restart on its own but spontaneous respirations can take longer. Thus CPR can be very beneficial until the person starts breathing on their own.
Although rescue and life saving is best left to the professionals, early after the event chasers can be very helpful. Once the authorities arrive, check in and find out how to best serve the area.
One thing to be aware of is the concept of triage. Others who are trained in this will understand what I'm saying, but to the general public, what I'm about to say sounds callous...it's not meant that way at all.
Generally, in a mass casualty incident, it is not considered the best use of limited resources to try to save a person who is pulseless, for whatever reason they became that way. Because of the situation, you sometimes are forced to leave the side of someone you'd normally do everything within your power to save.
The people you can be most effective in saving are those who have suffered critical trauma injuries -- those where you can apply direct pressure to stop bleeding, as an example. CPR is a good skill to have in these situations, but the reason is not as you'd expect -- knowing how to accurately asses a person who is down can save you from wasting resources that can be used to save another person who has a chance at life. The most life-saving knowledge you can have in a mass-casualty situation is basic first-aid, IMO.
[Edit: For clarification after reading Dr. Persoff's posts] I don't disagree with anything he's said. If you're faced with the situation where you have to choose to do or not do CPR, you're in between a rock and a hard place. Start it, and you don't have the personal authority to stop it until the person revives, you collapse, or you are relieved by someone with equal or better training than you. Don't start it, and you may be wasting the person's one chance at survival. A compromise -- if you know CPR, you can teach someone the basics very quickly -- "push his chest this far, several times every 10 seconds, and don't worry about breathing for him. Keep doing it until you're relieved or he revives." Once you have enlisted someone else to do it, you can continue to help others.
Okay, now I feel like I'm going in circles...mass casualty triage is one of those things that's not easy to explain to a general audience, and no matter what decision you make, IMO you'll find something you did (or didn't do) to regret. I've never had to make the decision not to treat someone, but I imagine it would be one of the hardest of my life.