There are two ways to connect external runtimes to Poser, manually using the plus sign in the library, and automatically with the built in Python Script.  In either case, yes you can connect external runtimes from other drives to your library. 

And just to clarify on SSD's, some reports have revealed that those drives are prone to failure if data is constantly written back and forth on a regular basis.  IIRC, some failures have been noted as early as 6 months.  It would be best to keep your content on regular external disk drives to ease the burden on the SSD.