I’m actually going to say no, it’s not. About 25-30% of my LD’s are from WILD. Only a couple of those have started with SP. It’s true, your body will enter SP any time you’re dreaming, but it doesn’t mean you have to go through it consciously. Part of it depends on when you WILD. If you try at the beginning of the night, it’s more like for you to hit SP. If you’ve been sleeping for a while first, you’re more likely to skip that step.
I will say that SP is a very easy way to get WILD, though. If you get SP fairly frequently or know how to induce it, by all means go ahead.
I go into a little more detail with my article here.