We are working on LimeSurvey integration with MODX (only in integrating users with the token code for surveys into the MODX user system so only certain users can fill out certain surveys). Usually, we install LimeSurvey alongside MODX and call up the surveys in a lightbox.
If you have a plan, is one free to create additional databases and install additional applications such as LimeSurvey?
I've installed the Vanilla forum with no problems, although I did use the same database. Unless you have a really busy site, using the same database is not a problem, just use appropriate table prefixes.