Militarily? Sure. They have a common threat.
But a political union seems unlikely, given the huge culture difference.
I've actually been wanting to comment on this for some time. Hammerfell has been believed to lean more toward the Altmeri religious position in the past (emphasis on Satakal, revilement of Sep/Lorkhan, end goal = the "Far Shores", or Aetherius, etc.). That they have ended up one of the main stark enemies of Thalmor is... interesting.
I mean, hell, most of TES III: Redguard was fighting the agents of Tiber Septim the mortal.