I had a similiar situation and I came up with jimmy rigged
solution. This might work for you.
I created htm topics in RoboHelp that contained key words of
a corresponding ASP page. If, for example, your ASP is on widgets,
you could create a topic with some hidden text about widgets. Then
make this HTM topic a automatically redirect to the ASP page. When
the user searches for widgets, they'll hit this page and
automatically redirect to the ASP.
I know that this isn't ideal, but so long as you take the
time to clearly define the text in the HTM, it might work for you.
Cheers