I went from RH6 to RH7 a few weeks ago and had zero problems
related to the transition to the help itself. However, I did
(temporarily) break our software build process. When the developers
installed RH7 on our build computer, we had to sort through some
issues related to the upgrade--nothing terminal, but it was a
headache for the first few days. Depending on how and where your
help gets built, this probably won't be an issue for you--just
something to consider (I didn't)....
Also, if you're really worried about the transition, make a
copy of your RH5 project, download an eval of RH7, and test to your
heart's content. I did this before upgrading and I'm very glad I
did.