First of all, why never curl? The curl itself is not a problem, it is the over use of it. A few sets a week can’t hurt.
To answer your question though, yes. Do a variety of curls. I tend to stick with hammer curl, both incline and cross body, and dumbell preacher curls.
I could be wrong, but I figure if biceps are your weak spot during pullups and snatches (where your hands are pronated) you might want to think about reverse curls.
Your hips are supposed to be the prime movers when you snatch. I don’t see why biceps would be a problem.
As for pullups, I’d rather you do close grip lat pulldowns with a supinated grip instead of curls. Make sure you get a good squeeze when the bar reaches your chest. Seated rows also help, especially if you squeeze in the fully flexed position. In my experience, I feel my biceps more here than when I do curls. I also get the added benefit of actually getting stronger in pullups.
If you still wanna do curls, I suggest you do one variation and stick to it. I assume your goal is to get stronger, so concentrating on one movement and getting your numbers up would be a good idea. Gironda perfect curls are a great way to put tension in the biceps throughout the whole ROM. This will help you in the top position of a pullup.
Forearm: Zottman Curls (Hard to explain on paper), Reverse-Grip Curls, anything where you use your grip strength.
A lot of people only do wide grip barbell curls because that’s where they’re strongest and only do suppinating Dumbbell Curls because that’s the way they see everyone do them. You should do a variety of arm exercises in order to get the best results BUT if you’re just trying to look like a badass and you want to work all the parts of your elbow flexors then do Hammer Curls and Wide-Grip Barbell Curls. Hammer Curls are cake. I can do pretty strict Hammer Curls with 65lb dumbbells and my arms are tiny.
In addition to adding in some curls, try doing some heavy negative chins/pullups. Use a box or bench to get in the top position, then lower yourself slowly.
Curls will help to an extent, but if you want to get stronger at the top of pullups, that’s where you should train.