A Visualforce page that uses OAuth for authentication configures it at the page level, and uses OAuth for all JavaScript remoting requests. Other than configuration, using JavaScript remoting is exactly the same.
<script type="text/javascript"> Visualforce.remoting.oauthAccessToken = <access_token>; // ... </script>
oauthAccessToken is an OAuth authentication token obtained by your page’s code. Obtaining and updating an access token is straightforward OAuth, with one addition. JavaScript remoting OAuth authentication requests the “visualforce” scope, so your token must be generated with this or a scope that contains it, including “web” or “full”. Set scope=visualforce (or “web” or “full”) in your OAuth request.
For information about obtaining access tokens, and using OAuth with the Force.com platform, see Authenticating Remote Access Applications in the Salesforce online help and developer.salesforce.com/page/Digging_Deeper_into_OAuth_2.0_on_Force.com.