I am not aware of any tool that does what you want with RoboHelp but I wonder if there are such tools more readily available for Word. If there are, you could generate a printed document and work with that.
Please follow this link and submit a feature request. Make sure you mention Flare has such a tool, albeit a chargeable extra.
See www.grainge.org for RoboHelp and Authoring tips
You can also use the W3C Validator to check for problems in the HTML. It’s under File > W3C Compliance.
As far as I see, what Flare Analyzer offers is offered in RoboHelp under reports and in the project manager. (Broken links, missing images, etc.)