The debian package manager (dpkg) is certainly one of the safest ways to update your software. If you did not add third party repositories to apt and follow the stable releases you shouldn't experience issues as all updates and new software are tested for long before they reach these repositories. It's considered one of the most stable distros, but remember that it can't be bugfree in every possible situation.
You should be ok just by using
apt-get update and
apt-get upgrade, as the
dist-upgrade variant will be "less caring" regarding dependencies. Also every file is checked for changes or if it already exists before overwrite, so it will ask you before pretty much anything that could break your proprietary driver.
Also consider that drivers on linux are compiled as kernel modules, so an extra care could be to blacklist the nouveau driver so that it will never load even if installed. Nvidia most certainly has debian on their test list to make things better.
In general you should be safe, but nobody can guarantee you that and having third party software will increase your chance to experience issues, whichever they are.