Is there a way to include html file or snippet directly in jade?

You should be able to simply include it within a jade template:

As mentioned include can be used to include other content such as html or css. By providing an extension, Jade will read that file in, apply any filter matching the file’s extension, and insert that content into the output.

html
  // ...
  body
    // ...
    //- html files have no filter and are included verbatim
    include content.html