I don't think it is a problem to answer a question and include a link to one of your hubs. In fact, HP gives you an option to answer a question with a Hub. What would be the difference in writing a hub or providing a link to something you have already written? If you have already written something similar to the answer, why wouldn't you save time by providing a link?
It also saves time to provide a link rather than typing in the same information that you have already written.
Finally, sometimes you maybe aware of another hubber that has already answered the question with a hub much better than you could and you provide a link to their hub.
Anyone that reads your answer now has a choice. If they want more information than your brief answer, they can go to the link. If not, that is fine too.