Could the borg assimilate the dominion into the collective,the jem'hadar would be great tactical drones or would the borg have a hard time tiring to assimilate them?
If the Borg saw them worthy of perfection they would go after the Jem'Hadar, Vorta, Changelings and any other member of the Dominion they wanted. A Borg-Dominion War would be a devastating event though, very epic to see or read about, but I doubt there would be little left of either once the dust settled--no matter who actually 'won'.
yup http://www.trekbbs.com/showthread.php?t=214996 The borg would deffinatly go after the Dominion as they would see them as a threat. Thats why they went after the federation even though they were tens of thousands of light years away from there space. No if the borg sent one cube to the federation Im guessing it would send a fleet to the dominion seeing as they are many times more powerfull. Like wise the founders would see the Borg as a threat and we all know what the dominion does with threats.