Neither of the two original words in question (joder, vaina) are curse words in DR. However, they are crude words used more commonly by uneducated people. They should never be used in a formal or business setting, as it would be considered low class.
Joder generally translates to bother. Examples: No me jodas. (Don't bother me.) Ese muchacho si jode. (That kid bothers a lot. {is a pain in the a$$}) In other situations, it can have other meanings, such as: La nevera se jodio. (The refrigerator broke down)
Vaina has no exact meaning, and it's commonly subtituted for an object/thing. Examples: Pasame esa vaina. (Hand me that thing)
Again, keep in mind that we are talking strictly about DR. These words may and do have totally different meanings in other Spanish speaking countries, and if you use them as you would in DR, they may not even make sense.
Thanks for backing me up on this.