Yes you can. The first thing is when you publish your project, make sure that you choose the "Build to view offline" option. This will roll all the Flex Framework into the resulting swf. This will be mean your resulting swf will be larger. Also note that your FLA must use ActionScript 3.
Here is some sample code to load the swf into your Flash Professional project.
var ldr:Loader = new Loader();
var url:String = "Main.swf"; //The Catalyst made swf
var urlReq:URLRequest = new URLRequest(url);
Hope this helps.