Subversion - Homebrew vs. Xcode command line tools
No, there shouldn't be a problem having 2 different versions of Subversion installed at the same time. MacPorts and Homebrew will install their executable binaries to a different path.
The version which actually gets executed when executing svn in the shell depends on your $PATH environment variable, which contains a list of directories to search through, in order.
If your $PATH variable lists the directory where Homebrew installs binaries first (I believe this is the default configuration), svn will use the more recent version.