It's possible a keyword could be related without actually being in the article. For example, an article about truck drivers uses the word trucker instead of truck driver. Both are still relevant keywords. I would say if a word is worth being a keyword for your article then you should work it into your article as well.
I know Google has an way of telling related words like this so it's unlikely they would penalize you for related terms.
If the keywords are not related it will harm your SEO efforts rather than help. In other words, irrelevant keywords are worse than harmless... like WryLit says, they could get your hubs reported or unpublished.