It depends on the loader. Some will load a VST from anywhere you want, some will display a list of VST dlls that are in a folder (and it's sub folders), and some will do both.
I keep all my VSTs in C:\Program Files\VstPlugins and then I don't have to bother with which way any of them work, works for both styles of hosts.
I keep all my VSTs in C:\Program Files\VstPlugins and then I don't have to bother with which way any of them work, works for both styles of hosts.