Just because a plant is blooming does not mean that it has both nectar and pollen or either for that matter.
Most of our southeastern nectar producing plants are done for the year or at least until fall when the goldenrod and aster come in. Now of course most anything that blooms does rely upon pollen for reproduction so pollen will almost always be available in some form as long as something somewhere is in bloom, though bees do not use all pollens the same. They have their preferences just as we do.
Nectar is also highly dependant upon available moisture. It takes alot of water to make nectar and the southeast has two peaks of available rainfall during the summer bloom season, spring and fall hence our two peak flow. This is also a reason why flows can fail from year to year if we miss the rain at the right times.
Before I would feed I would see if they had any capped honey or nectar curing, if so they will be fine without feed. If they do not then by all means feed. Their nectar/honey needs are lower this time of year as they are not burning pure carbs (honey) just to maintain warmth as they will come winter.