When you use nutrients and energizer the fermentation is going to be faster with a much lower chance of not starting/stalling.
That doesn't mean that you can't do it without them though, much depends on the initial gravity and the yeast you use.
I've just accomplished a full fermentation from 1.145 to 1.019 (final ABV ~17%) using DAP and boiled bread yeast, but I've used a champagne strain with very low nutrients requirement and anyway I've followed the staggered nutrients protocol.
I think that for high gravity meads using some kind of nutrients (raisins, boiled bread yeast) together with diammonium phosphate is a must, since honey alone can't feed our microbes properly.
On the other hand there are many brewers preparing show meads using only water yeast and honey, but reading about incomplete or slow fermentations is very common.