The SimpleChart widget is entirely based on JQuery, so it is perfectly possible.
Just put an dojo.provide("mymodule.jquery") on top of the jquery file, and in the header of your widget put dojo.require("mymodule.jquery"). Dojo will make sure that JQuery will be loaded when the client is loaded.
To prevent issues in the future, you might want to check whether jQuery isn't loaded already by another widget before requiring it. Further, my advice is to use 'jQuery.xxx' instead of '$.xxx' throughout your code.