No I downloaded the CS5.5 creative suite a few years ago. Although all the products are CS5.5, for some reason Encore is CS5.1. I'm sure why that is, but the library is completely empty.
Encore was not a "full" upgrade, so it got a minor version increase. But the bottom line is that the version of Encore in CS 5.5 is Encore CS5.1.
An oddity of the Encore CS6 library install is that it REMOVED the library for CS5.1. Never did figure out what the logic was or whether it was a bug. A real mess.
But the bottom line for you is to use the CS6 library but install it using the following method rather than the dmg installer.
Encore Help | Download full library content/functional content
This method just involves extracting it and putting the folders in the right places. In addition to the library folder, you can also put the styles (fonts etc) and templates (flash export) in.