Most Nuke modules / functions display the HTML as it is build, rather than using a template approach where the HTML is stored in a variable, then displayed at once.
I'm not familiar with Gallery, so I couldn't tell you off the top of my head which approach it uses.
Basically, you'll need to replace the textareas where you want the editor to appear with one of the two approaches. If you post some my_egallery code examples, I can walk you through it.
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