Windows 8 hasn't been officially released yet so officially RoboHelp 10 does not support it. That is not the same as "does it work with RH10" though. To be honest I don't think anyone here will know the answer to that question until they get their hands on Windows 8. Adobe will be aware of Windows 8 though and if they think that the current RH version has issues with it, we can probably expect an update to RoboHelp 10 before too long. This would more than likely not be a new RH version, but a 10.1 version though.
As Windows 8 has not been released, I'm not sure any vendor would guarantee that their product will definitely work under Windows 8 - it is always possible that Microsoft make last minute changes to the build. However, for your reassurance, Robohelp 10 was tested with Windows 8 BETA builds and at the time updates were made to accommodate this new version of windows.
That is the best assurance you will get at this stage.
I'll be upgrading to Windows 8 as soon as it is launched in UK.
Thanks for your help everyone.