There was a FAQ that recently clarified how Blessing of Fervor and Haste stack. If they choose the AC bonus from BoF they don't get the extra attack from Haste on that turn. However, they can choose one of the other effects of BoF that doesn't overlap with anything granted by Haste.
Similarly, blessing of fervor does not stack with haste, which means that the increased speed, extra attack, and attack roll/AC/Reflex save bonuses wouldn't stack between the two spells, but if you had both spells active, you could still get those three benefits from haste while choosing to stand up as a swift action or apply metamagic to a low-level spell.
But hey, at least you don't have a Paladin with stunning critical. He hit Delvahine on the first round, she failed her save and became stunned. The party cleric stunned her again, sending her to stagger. She was stun-locked for the rest of the fight.