Not sure, not a feature I use or have tested.
Download the merge demo on my site as it is small, making it easy to set up a test. Let us know the result.
See www.grainge.org for RoboHelp and Authoring tips
After playing with the small demo in RH6, you can't automatically do See Also between merged webhelp projects. In the Webhelp See Also button dialog box, there is no option for Remote See Also Keywords.
However, if you feel masochistic, you can hack the output files.
I did think of a sort of work around using redirect topics, although it works out more like Related Topics than See Alsos. Might be okay if there aren't a lot of links between projects...
I'll use the "parent/child" terminology as per Peter's merging tutorial. Plus I haven't worked with this except in the sampel project, so I haven't discovered all the problems associated with larger projects. Consider it a thought experiment.
1. Create a topic with the same Title as the topic in the other child project.
2. Remove all content from the topic.
3. Switch to code view and add the following script:
The path should reflect the output path, so for example if you are working in child_2:
4. Assign the same See Also keyword as assigned to the topic in the other project. It probably doesn't matter, but I suspect it will help keep track of what you are linking to.
5. In the topic with the See Also button, add the See Also keyword to the button.
I think I'll submit a feature request tomorrow and see what Adobe says.