I have used green pine and green oak pegs, drawn, with no noticeable issues. Some times the pegs have been made ahead of time and other times they were made the day before raising. I have also used tamarack for pegs.

My Mom relates a story of when she was young and recalls her dad going to work. He worked many different jobs, in this case he was working on a barn, 1940's or so. It is not known if he lead the group of carpenters or was just a worker, but he was the oldest of the crew by many years. I had a chance to view the barn a few years ago. It was a combination of mortice and tennon and balloon/stick framing. The pegs appear to have been made from broom handle stock. This is a good example of mortice and tenon work still being used well into the 20th century.