[CentOS] Add new app to repo & db install question

I've got two questions that I'm curious about. One of for the maintainers of CentOS and the others is for the community at large.

1) At what point does a third party app get rolled into the production repository (not sure if I said that correctly)? Example: At what point is it OK for the OS maintainers to adopt a newer version or PHP, MySQL, Apache, etc.?

2) I have read mixed opinions with how to install a database server. Some articles say install it via YUM for compatibility purposes; while others say install it from a tar ball or source to ensure other packages do not try to upgrade and break the database. What are your thoughts? I plan on running a web server farm for a CMS/DB that needs to have a five 9 uptime.