No, he isn't.
This has been confirmed and explained by Robert Jordan himself, see point 23 in this interview report from Theoryland:
Is Olver Gaidal Cain?
RJ: No. I didn't really think that this would last as long as it has. The timing is wrong. He has another reason for being there besides being a red herring, though.
He's too old.
RJ: Yes. Time in Tel'aran'rhiod and the real world run at different rates, but it never runs backwards. You may spend an hour in Tel'aran'rhiod, and a day has passed when you get back, or you may spend a day, and an hour has passed when you get back, but you'll never go in on Tuesday and come back on Monday.
Is the difference in time constant?
RJ: No. It's fairly random. Sometimes fast, sometimes slow, sometimes the same as real time.
It's different for different people, then?
RJ: Yes. Unless they're together in Tel'aran'rhiod. Then the same amount of time passes for them obviously.
So what specifically does RJ mean by "The timing is wrong"? Well, one of the first times Elayne meets Birgitte in Tel'aran'rhiod, Gaidal was also there (and disapproved of Birgitte speaking to Elayne); so he must have been reborn after that time, both in Tel'aran'rhiod and in the waking world. But Olver is much more than a year old, so he must have born years before even the start of the WoT series. Thus, Olver cannot be Gaidal Cain. QED.