No, you don't have to USE MPLAB X but you need to have it INSTALLED so that you have access to the assembler that comes with it. And, it doesn't HAVE to be the assembler from MPLAB X, it can be an older version from MPLAB 8 but then it won't be able to assemble programs for newer part.

So, if you haven't installed MPLAB X then do so. I Believe the plugin you mention is when you want to so the reverse, ie use PBP as the compiler from within MPLAB X.

/Henrik.