Effective in capturing? Proly not.
Effective in stoping a fight? YES!
When only 2 FHs are up and there is no capture attemt, there are no osties on the ground (since no enemy plains are vulching or trying to cap). So, diving in and droping, even as you die, will take the last FHs (or the CV) down and stop the fight. Mission acomplished.
If you really want to know how effective they are, ask an expert like 999. Only, he does not really dive bomb the CVs. He flies level over the deck (so technicly it is not dive bombing) and drops his bombs as he dies in the puffy ack. He will die 10 times in a row, but eventually, the CV will go down. Mission acomplished.