Thank you for considering and evaluating Sitefinity. Actually, we have encountered no case of applying Sitefinity for help authoring up to now, and have therefore not prepared any documentation on the topic. This is a new approach to applying Sitefinity and we are more than eager to cooperate with you in exploring its advantages.
As to your question on generating a keyword index of topics - there is currently no ready-to-use tool to do that. However, the technology we are using for our search module could be applied to extend the current functionality in the desired direction. We use Lucene.net and it should be possible to use it to generate a list of keywords. Note that we have not yet tried that in practice but it is theoretically achievable.
Please contact us if you have any further questions. Also, it is important for us to receive feedback about our CMS in the future in order to make Sitefinity a better tool for help authoring.
the Telerik team