Is it possible to generate UML, and maybe more documentation, from a Symfony 1 project?
Documentation can be generated using PHPDocumentor, for example. About UML, please, see this: PHP UML Generator
ORM Designer was of great help to me to visualize my Doctrine schema. Though not so qute as MYSQL Workbench, but it was able to parse the schema and visualise relations correctly.
Designed for windows, but works good under wine on Linux.
This can help you convert a Symfony schema to an UML: http://xpt.sourceforge.net/techdocs/language/php/symfony/sf14-Database/ar01s05.html