I'd have to follow with your example of Olidammara and Heironeous - I'd rule that it depended on if the dominated Cleric was still acting within the dictates of his faith (and/or alignment) or not on whether his Deity granted spells for the day.
It also depends on how heavily Deities influence your game I guess. If they are just a name on the character sheet then there probably won't be much of a conflict. I like to bring everything of a character into play at one point or another, especially flaws, so your Deity choice plays a big part in my FR games.
I've got one very pious pally in my group who is always calling praises to his deity and trying to spread awareness of him - so when he was all set up for a charging smite attack with all his crazy charging smite feats he's got and he missed the target AC by 1... his Deity's hand guided his lance on target for the strike. Every once in a while I like to play in some divine intervention type stuff so Deities become more than just a name on the paper, there have been some negative influences when they make their Deities mad too though.
