Found excessive tree sap oozing out of the rafters in an attic. It was hard and dry. However it was also 30 degrees outside. Is this an indication of improper venting or just a common occurrence with particular types of wood?
That piece of wood will never rot. I never consider it a concern.
Well my concern is not that it will rot but if its an indication of inadequate attic ventilation that will result in an premature roof deterioration, energy bill increase and the A/C to be over worked. Is it a concern in that sense?
No…the sap is quite common from what I have seen over the years.
No. Some wood has an abundance of sap in it. It cooks out in the heat and eventually crystallizes.
You should be able to determine the adequacy of the attic ventilation by direct observation of the ventilation system.
I looked at your photo. I’m guessing by the plank board roof, that the home is 1950’s or before. I also bet the ventilation sucks, because most dont have adequate ventilation. Many dont have soffits.
With that said, your climate is not going to overwork any a/c or cause large energy bills. I would be more concerned with the winter months. Come on down here and you can see some overworked a/c units. 
Did you find anything else concerning heat in the attic?
It takes more than one issue or one trip to the property determine cause.