Basically, the answer is no.
The reason is that Expressor only works with a specific release of Subversion, which is not the most current release.
Trying to use an existing Subversion install as the repository will most likely not work since it is unlikely you have the proper version installed. And, even if you have the proper version, tying Expressor to this install would prevent you from upgrading your Subversion.
Finally, an existing Subversion install would not include the command line executables you need to manage, for example back up, repository.