Anyway, how I would adjudicate the OP's situation:
The summoned whatevers would attack the hobgoblins.
As noted above, Despite rushlight's protestations to the contrary, they were in combat because they were readying actions. That makes it pretty clear that they are enemies, IMO.
As for the various bless questions:
As I see it, with bless and it ilk, there are no
in game world decisions to be made. The magic just works.
Outside of the game world, the DM decides who get the bonus. The DM knows what the potential allies/enemies attitudes and intentions are.
Hostile doppleganger (invisible or otherwise) -if he's hostile, he's not an ally, so no bonus.
Polymorphed party member -unless the polymorph has affected his mind so he no longer friendly, he is still an ally and gets the bonus.
EDIT: Wow, three posts in a row. I must be talking to myself
glass.