Let me get this straight... you want to use the same line of code:
placebomb = vehicle addaction ["place bomb","bomb.sqs"]
On a bunch of different vehicles? Like this?
placebomb = vehicle1 addaction ["place bomb","bomb.sqs"]
placebomb = vehicle2 addaction ["place bomb","bomb.sqs"]
placebomb = vehicle3 addaction ["place bomb","bomb.sqs"]
And you want to know if placebomb will have the right action ID for all the vehicles? Is that right?
Well, obviously placebomb only contains the action ID of the very last action added, since you overwrite the variable each time except the last. So the answer is, not always. It will only be the same if all the vehicles already had the same number of actions added before you added this action to them.
Is that what you were after? I'm not really sure I understand...