Most probable it's because it's not compiled to work with SketchUp Ruby.
(Is it even a match for SketchUp's version? 1.8.x?)
One possible cause for the crash could be that it is not compiled into a flat namespace. See my SketchUp Ruby C Extension Hello World project for notes on compiling for SketchUp Ruby:
https://bitbucket.org/thomthom/sketchup-ruby-c-extension/src/5c9eb31c541b/src/Example%20-%20Hello%20World/extconf.rb
@unknownuser said:
<span class="syntaxdefault"> </span><span class="syntaxcomment"># Must be compiled into flat namespace. Otherwise SketchUp Bugsplats.<br /></span><span class="syntaxdefault"> CONFIG</span><span class="syntaxkeyword">[</span><span class="syntaxstring">'LDSHARED'</span><span class="syntaxkeyword">]</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> </span><span class="syntaxstring">'cc -dynamic -bundle -undefined suppress -flat_namespace'</span><span class="syntaxdefault"> </span>