Do you need to physically demonstrate peeing in the toilet to potty train your son?

No. Generally they can model what they see and by that age, what they are taught. Remember that true training probably does not occur until the child can not stand being wet and wants to avoid it no matter what they are doing. A child who does not care if they are wet or dirty has no real motivation to stop other more fun things to stay dry.
No. Moms of children with absentee fathers have been toilet training their sons for generations without difficulty. Your son should have no problems.