Is it at all advisable then to use these SVN binaries in my situation?
The only thing that can really mess up your player is bootloader installation. There are players where the risk for this is almost zero (for example, you can't trash an Ipod by installing a wrong or broken firmware on it, you can always restore it with Itunes). Other players (like the h100 series) can get seriously messed up when installing a broken or wrong bootloader. However, all installation tools that do have a release have various security measurements (like checking the original firmware file before doing anything) so the risk should be fairly low in any case. Nevertheless, unless you install the bootloader using Rockbox Utility from svn is safe. As you want to install the voice file there's not much that could go wrong (except the voice file not working of course).
In short, using svn binaries of Rockbox Utility is pretty safe for everything that can't mess up your player, which is everything except the bootloader installation. Worst should be to loose your installation and having to reinstall Rockbox.
If yes, how do I install them, or should I re-download the RB Utility (provided the patch has been incorporated therein)?
You don't install Rockbox Utility. Download the zip file, extract it and run the binary. It's the same as for releases (those binaries are built exactly the same way)