Please let me add some detail to this.
There are several commercial implementations of open source projects, such as Subversion, and we can't certify them all so we validate our development against the open source versions as indicated in the documentation. Since most of our actions address common use cases leveraging common methods in the open source API, those should be compatible with most commercial implementations, if those vendors have not made modifications to the API or the configuration. While we can't explicitly state support for that specific vendors implementation, we would be willing to support your use of the actions against any compatible Subversion implementation. We can only replicate issues in the specific versions and implementations (open source) that we state support for in the documentation. We can't support WANdisco SVN Multisite specifically, but we can support Subversion.
I happen to know some of the R&D folks at WANdisco and they are major contributors to the Subversion project. While we may not support the extended features of their implementation, you should expect to find compatibility with our actions. I would appreciate any feedback that you can provide from your testing, so that you can share your learnings with the community. If you run into issues, let us know and we'll make a best effort to assist.