Hmm... Seems to be working with SVN without the FreeBSD template patch. So either before I handled going from CVS->SVN wrong, or the FreeBSD folks now apply their own patch to svn no matter what and made the template portion optional. By CVS->SVN, you don't mean previously having /usr/src as CVS and then doing a "svn co url:/path/to/whatever /usr/src", right? I believe svn will still complain if you try to checkout to a populated directory (I generally use git these days so I'm a little rusty). Or do you mean simply getting rid of the cvs'ed tree and going with svn? Looking at the source files, it doesn't seem like that will be an issue either... guess I'll get back to you on this after rebuilt everything with the latest source.
I think we're talking about 2 different things... when I initially did a svn checkout a few years ago (without specifying to use the FreeBSD patch) of the source years ago... the tags in the files were wrong... Instead of having numeric values, there were just questions in their place. I had to recheck everything out using the patched svn. I then found that ports still wasn't available via svn so I decided the whole thing was half-baked and went back to using cvsup. I'm using svn to checkout the source while I type this post, and so far it seems the tags have the appropriate values so it seems no freebsd patch is needed to properly check things out properly anymore (the template patch is if you're a FreeBSD dev for those who don't know).
Anyway, so having the tags in the files having question marks instead of the proper values is what caused the issues with mergemaster. Mergemaster uses those tags to determine whether the file may or may not needed to be updated. Mergemaster is the FreeBSD equivalent to Gentoo's etc-update. I'm sure you know all of this, but I'm putting it here for informational purposes.
From what I remember from years ago, If you've been using CVS, then all the files in /etc will have different version headings than SVN (e.g. something like $CVS Id ... blah blah$). The first time you use SVN, mergemaster will inquire for every single file in /etc since the version headings for SVN are different. You'll only have to tolerate this once though.