No. The downloaded nVidia installer copies over the various OpenGL libraries and some other system libraries instead of linking them through the alternatives system as a good package would do. It also clobbers some of your system configuration files. It's fine if you never want to remove the package or even upgrade properly, or if your preferred method of upgrading is to wipe the disk and reinstall, but if you're used to smooth problem-free upgrades, or if there are bugs in the nVidia driver (and there often are in releases that have not been tested by the Ubuntu package maintainers), you're in for a bad time. If you use your system for work and need to rely on it, stick to the Ubuntu packages.
In my personal experience I've never had any problems updating from the nvidia site, which I do every couple of months. But on the other side, I've even ended up once with a unbootable system only by installing from ppa.
In 13.10, using default repos, I've ended up with a huge boot delay of around one minute! That's why I needed to go back to 13.04...sigh a huge mess that should be fixed.