If you are doing manual tagging to train your own NER model (it's not 100% clear from your question), you should include the same kind of data you expect to tag later, most likely full sentences. The default model features (see OpenNLP docs) include a window of tokens to the left and right of the token that's currently being considered, so you want your labeled entities to appear in their normal context. You also want your model to learn which words shouldn't be tagged as entities, so they also need to appear in context in your training data.
See the related question: Open NLP Name Finder Training