Is WooCommerce required to use the Group Registration plugin?
You can use the group registration plugin without WooCommerce as well. You need WooCommerce to sell the courses as products. However, if you are selling the courses by some other methods or not selling the courses at all then as an admin you can manually create group and assign an user as the group leader. You can set the group limit from the LearnDash->Groups from admin dashboard in the 'Group Registration Left' option.