It doesn't matter.
The SI range of Cakewalk vsti's was introduced, I think, for X1 and haven't been changed for X2
The dll's for all the SI range at least for 64 bit, are installed under their own names in C:\Program Files\Cakewalk\Vstplugins. There is a folder for each one Bass Guitar, Drum Kit, Electric Piano, String Section
For 32 bit systems the dll's should be under C:\Program Files (x86)\Cakewalk\Vstplugins.
I'm not entirely sure what you mean by
"not listed in VST plugins or anywhere else"