Totally not necessary. Especially if he is already adjusted to sleeping in the dark. Our kids both went into the crib in the nursery with NO nightlight from day one, and we never changed it. There has always been a "nightlight" over the stove in the kitchen though... and it is sufficient for ANYone who needs to get up during the night.
If you introduce the nightlight now, because YOU think it would be good/fun/helpful then you are just asking for issues later on... when you travel are you going to always pack a nightlight? What if it burns out and you don't have a replacement bulb.. are you prepared for a meltdown over something like that at bedtime some night when you are least prepared?
Why introduce the issue?
Also, it has been shown that ANY lights in the room, disrupt sleep and sleep cycles... including those glaring digital clocks. :(
If you want to put a nightlight or two along the walk he would have to make during the night to your bedside if he felt ill, then that is a different matter altogether.