Does anyone know if it is possible to copy raw MySQL data files from RHEL5 to RHEL6. From what I understand, MySQL GNU C Compiler and integrated DFP support with it. Would this make it incompatible?
You can use binary copy of your MySQL data across any Linux platform. I don’t think there is any incompatibility in GNU C that would make any problems. Of course you must stop MySQL server to make consistent copy, or use online backup tool like Percona XtraBackup.
You can also use the same tarball MySQL or Percona Server distribution on both RHEL5/6 or Centos5/6, but regarding the RPM packages, use the dedicated ones.
One important detail that I left out was that the source server, RHEL5, is running MySQL 5.1. So I am guessing that I would need to get at least get my source server on MySQL 5.5 before I could even consider the copy, correct?
Not necessary. You can perform the upgrade on the destination machine. Once you’ve restored to the 5.5 instance run the mysql_upgrade script. http://dev.mysql.com/doc/refman/5.5/en/mysql-upgrade.html
I thought about doing that, copy the binary files from MySQL 5.1 to MySQL 5.5 on RHEL6 and then run the upgrade script. However, that seems to be very outside what Oracle recommends for doing an upgrade from 5.1 to 5.5; dump data using mysqldump and restore.
For many cases binary copy and mysql_upgrade on 5.5 will just work, however indeed the safest and recommended way to upgrade 5.1 to 5.5 is to make SQL dump and restore. There are some incompatible changes and edge cases you may hit, this article is pretty long: http://dev.mysql.com/doc/refman/5.5/en/upgrading-from-previous-series.html
Btw there is faster tool then mysqldump out there, try https://launchpad.net/mydumper