A hook in muay thai is not a hook in boxing. They are performed differently and play slightly different roles. I'd say that yes they're important and are probably one of the most landed shots, but technically you don't "need" it. But are you doing it right?
Lead hooks in muay thai are done with weight on the front leg, and no foot pivoting. Waist and hips are engaged, but you're not going to sit down on the punch or pivot on the ball of the lead foot. The lead body hook is done the same way, no elevation change of the body. Just punching with the arm down a little lower. Rear hooks are done with the same motion a nak muay would use for a cross or rear straight--except you're throwing your arm in an arc. See a theme? In fact almost every single punch in muay thai has a tall, front weighted stance under it. The only nak muay that don't punch like this are typically ones that come from gyms with more modern boxing infused within them or ones that have trained and competed in western boxing. Now strategically hooks in muay thai are generally used in combination off a rear straight, and precede such things as the rear diagonal kick. They'll also be used as counters to the lead round kick (for example side stepping a lead round kick and having the lead hook hit as your weight on the front foot touches down, followed by a rear straight or rear elbow...knee...etc).
Hooks in boxing on the other hand, are done in a slightly lower stance. Lead hook is done by loading the front hip/leg/foot and that load is transferred to the rear hip/leg/foot as the lead foot pivots on the ball, hips engage followed by shoulders and the punch. Body shots are done in an even lower stance (elevation changes to suit the target elevation). Now with body shots opinions will vary on whether to pivot the lead foot based on intent of the punch, power output, spatial relationship and etc. Long story short some folks pivot the lead and some don't. For example while in the pocket you can throw a body left without pivoting on the lead and then a high left hook as normal. Strategically...hooks are my favorite weapon. They can be used long or short, as leads offensively interspersed with jabs, as counters defensively off a bob and weave...it's just an all around great punch and one of the best to KO someone.
As far as rear hooks in boxing, you'll hear some people say that they're non-existent in boxing. I beg to differ. They exist, but usage is a rarity in general. From my experiences, the rear hook is more commonly used either deep on the inside (in the pocket) to setup uppercuts and vice versa, or as a counter shot off a pivot when someone comes in hot. It's generally not used as a primary offensive tool (for example "a long right hook") from what I've seen. But I'm also not the most senior boxing authority in this sub-forum, and my experiences in straight boxing are not as complete as others here who's knowledge you can tap on that.