Your version of Sitefinity is not the problem here. Maybe something went wrong during the whole process which prevents the provider from showing. Most of the steps in the blog post are related to working with data in that provider. The only one that could have caused it to disappear is the one where you register it in web.config.
Please double check that the code from the blog post is present in your web.config (with the correct connection to your database). Then restart the application and if it still does not appear, send us the log files from the ~/App_Data/Sitefinity/Logs folder. There may have been an error that caused the provider to disappear.
Putting the connection string in web.config is a requirement for using additional providers. The DataConfig.config file is only understood by Sitefinity and it has a slightly different format for its own providers. Following the procedure from the blog post, you are making sure that any ASP.NET provider is mapped to Sitefinity, but moving the connection string is a requirement.
As for the Registration widget - are you using the Sitefinity Registration widget available in the toolbox, or a regular ASP.NET one?