SJS, I’m convinced that tandem nursing helped reduce jealous feelings between my two youngest. Newborns nurse so much & this created a special bond between the two of them. He had been nursing throughout my pregnancy (not always fun but this was perfectly safe for us), but it probably would be fine to let your son nurse if he wants to try. If he doesn’t like it, then he may not feel that he is missing much when the baby nurses.
But tandem nursing is not for everyone, and there are other ways to make nursing a newborn a special time for your older child. I used to tell stories & read books to my older kids; when I couldn’t turn the pages I’d let them hold the book & “beep” when it was time to turn the page.