This point has actually come up recently over on the Spartan forums. Here is the official clarification:
Spartan BrDoG wrote:
Hi,
Combining fire means that the Escorts can respond to an attack at the same time as the parent model, the Escorts can Link Fire with each other as normal (but not the parent model), but when firing at Rockets for example the parent model fires separately from the Escorts, but the Escorts can fire as well at the incoming threat (because they are part of the same Squadron but not completely so).
Alain.
What this basically says is that Escorts get to respond to attacks against their parent model, even if they are not directly attacked, and vice versa. So, for rockets or boarding, you would effectively get all 14 dice from your example, as there is nothing that says you HAVE to link. These 14 rolls technically represent the 8 dice shot from the dread, and 3 separate 2 dice rolls for each escort. However, with rockets and marines, there is no problem with rolling all the dice together since there is no DR to reach.
Shooting at a flying model with a DR (bombers, scout flyers, etc) is an entirely different story, however. You would get the dreadnought's
AA, and then in a separate roll you would get the linked fire of the escorts. In theory, you could roll 4 attacks; 8 for the dreadnought, and 2 for each escort. But these rolls would have to be done separately, and it would be very difficult to get 4 or 5 hits out of only 2 dice! Note that what you can't do is link the
AA from the escorts and the DN into one attack against the bomber.
Here is the pertinent thread, if you wish to see the whole discussion:
http://forum.spartangames.co.uk/smf/index.php?topic=8002.0