Can "sons of God" also be a reference to angels?

Yes. In Job 1:6; 38:7 reference is made to angels as "sons of God." 

"Now there was a day when the sons of God came to present themselves before the Lord, and Satan also came among them" (Job 1:6).

"When the morning stars sang together, and all the sons of God shouted for joy?" (Job 38:7)