You need to physically install the fonts but please be aware that CS5.5 is completely unsupported under El Capitan.
Unfortunately, you are on your own.
Where would I find the font folder that Indesign is now using?
It will use the same folder where all the other fonts are installed.
That said, if fonts work in other applications, you can put them into the fonts folder in the InDesign application folder.
Thanks Bob, that did the trick!