No you cannot keep the two in sync. In theory you could
create an external link but RH would likely "correct" it so that
the path is relative in the source. You would then need to output
to a folder at the same level as the source projects rather than to
the !SSL! folder. Finally that path would have to hold true
wherever the help is run.
The likelihood of that breaking is pretty good!
BTW. The problem is not the fact the document is on a
different drive, just that it is external to the project.
On searching, no RH does not search the target of links.
There's an article about ZoomSearch on my site and that can work on
documents inside the project.