I'm confused. Is this question about RoboHelp or Captivate? If it's really about Captivtate, why are you asking the question in a RoboHelp forum?
I got the information on this web that Captivate can publish to kindle via Robohelp.
so just would like to check that which version of captivate that can convert to epub format via robohelp.
Yes, it is possible to generate Captivate Demo in Kindle compatiblie output. However Captivate standalone cannot do it. As you read this blog, it was mentioned that you need to insert the Captivate published output(SWF file) in Robohelp and then Robohelp will generate the Epub output which you can further view in Kindle.
Robohelp will generate the Epub output not Captivate. Hope this answers your question.
From the Kindle Publishing Guidelines: “Currently, only Kindle for IOS supports audio and/or video content. Kindle eInk devices and Kindle Fire do not support Kindle Editions with Audio/Video.” - http://kindlegen.s3.amazonaws.com/AmazonKindlePublishingGuidelines.pdf
I am a bit confused by that post as SWF is not a supported video format of Kindle. Although MP4 is a supported format, which Captivate can also create.
ePUB output was introduced in RH8 (but much improved upon in RH9 and 10)