This 2 ways do not give you the same result at all!! The big problem will occur if you install 2 or more packages, in this case ICxxx and LDVxxx, with not equivalent release version, since newer released versions alway have newer peripheral utilities i.e. JRE, cdsdoc, etc. I think IC5+LDV4 is OK to be installed in the same dir, while IC446+LDV4 is not. In Cadence's document said, you have to install the newer version software into the new dir because it can't completely replace the old version when it is installed in the same dir.
I think if you are not sure whether your 2 packages are compatible or not, it's a good idea to install them in difference dir. Just set your environment to be able to access all executable directory.