The skill is not necessary when you are using the Hue hub. That said, if you have color lights it will not recognize them as color lights without the skill installed. I didn’t have it installed and couldn’t figure out why my Echo was saying they were not color bulbs. Installed the skill and it recognized them as having colors.
Over the last 6 months or so it seems like my Echos are much less reliable with my Hue bulbs and Wemo stuff (especially the latter). It will say a light isn’t available when it is in every other app and I am getting a lot of misunderstood commands. I will say turn off one light and it will turn off all of them. My Wemo stuff sometimes take multiple tries before it will work.
On the other hand, Siri is much more solid with both devices, so it isn’t Hue or Wemo that is causing problems, its something with the Echos.