updated by @rene: 04/26/17 11:35:19PM
In my opinion and experience, all (real) shamans are lightworkers and some lightworkers use shamanic techniques. I think the answer to your question depends on how one defines shamanism and lightworking. Specifically, what does a lightworker do?
If you look at the Wikipedia definitionof shamanism, the description in the first paragraph overlaps significantly with other modalities that I believe most people would classify as being under the lightworker umbrella, such as psychic mediumship and energy healing.
Also, I think it's important to note that shamanic techniques can be used by "darkworkers" just as much as lightworkers, but because the title of Shaman is generally bestowed by others and not given to oneself, true shamans tend to be the healers, the lightworkers.