Got far enough to attempt to access the SubVersion repository using a remote client. Tried:
%svn co --username admin
http://www.myserver.com/svn/repository somedir
and found "authorization failed" for user "admin".
The missing step is to enable a SubVersion login for a user. From the page "Virtualmin Virtual Servers" click the name of a virtual server that has SubVersion enabled and then "Edit Mail and FTP Users" and then click a user and say yes to "SubVersion login enabled?" specifying a repository.
After enabling SubVersion login for a user, I was able to access the SubVersion repository and checkout the empty repository.
Bottom line: A year ago, I tried to install Subversion on a Cobalt RAQ server and gave up. Now, thanks to Centos and Virtualmin, it's running without any headaches of compiling special versions of Apache 2.0, etc. Thanks Virtualmin!