I've watered then with a hose before and it hasn't upset them, but ours are mature and in the ground. If you've got a young'un in a pot maybe it'd be more sensitive?
It's an old thing in the ground that had been chopped down completely when I moved in, 7 years of re-emerged growth now. It just doesn't look very happy, going to keep watering and give a little top dressing of ericaceous compost. Rainwater butts slightly replenished after last couple of days.
I've watered then with a hose before and it hasn't upset them, but ours are mature and in the ground. If you've got a young'un in a pot maybe it'd be more sensitive?