This folder we call "the sniff pool" which is the home of all sniffs which we (re)implemented for our Coding Guidelines.
Technically its possible to use this as standard by PHPCS (phpcs --standard=TYPO3 /path/to/file), because its a own standard. But this is not recommended because this folder contains ALL sniffs for TYPO3v4, FLOW3, so the result of the codesniffer will be wrong.
For further informations please have a look at: http://forge.typo3.org/projects/team-php_codesniffer/wiki/Using_the_TYPO3_Coding_Standard