I am using Campaign Standard and would want to create the user profile and subscribe it to a service via an HTML page. for ex: If a user submits a form on the website then he/she is subscribed to a particular service/newsletter list.
Is there any other way of doing that other than using the REST api's.
Here is what you can do to subscribe someone to a service/newsletter:
using your own landing page (outside of campaign): you will need to use the API via Adobe I/O to perform the subscription.
using your own landing page: if you have a way to generate a file containing the new subscribers, you can import the file through a workflow and perform a mass subscription on a regular basis (every day or every 6 hours or so). This process is asynchrone but could still be a solution depending on your needs.
using campaign landing page (you can customize the content so it matches yours if this is just a matter of content): you can set the landing page to perform the subscription.