I've noticed that the "mysql55" RPMs in the standard CentOS 5.10 repository install everything to /opt/rh. Is it expected that an end user might change this location somehow? It creates complications when trying to build software that depends on the MySQL 5.5 files, for example.
This is a Red Hat Software Collection. It's meant to live outside the normal filesystem locations so as to not conflict with original system packages (in this case, the original MySQL 5.1). This means that, yes, you have to perform additional steps to use the software. See the documentation for complete details on how to use Software Collections.