Is generally installing standalone rpms considered 'dangerous'? Are these affected by any system upgrades, package upgrades etc.? How about dependencies and libraries?
Its is not normally a good idea to install stand alone rpms, only because it is difficult to keep track of all the dependencies. YUM does a pretty good job of handling that for you. It is possible to install single rpms using YUM by issuing the following command
#yum localinstall <packagename.rpm> --nogpgcheck
If at all possible avoid installing rpms individually.
Installing standalone RPMs isn't dangerous at all, and in fact, sometimes you can't install them with YUM because they aren't in any repos. The reason RPMS are a good thing (like any package where you use a package manager to control) is because the RPMs themselves contain a spec that describes everything about the RPM to the system. This includes dependencies, which programs are controlled, etc.
Both YUM and RPM use the same databases, so using YUM localinstall is ultimately the same as just running
rpm -ivh packagename.rpm