No, Gatling has neither.
Building a jmx converter is something we might investigate in 2013, as you're not the first one to ask for it. At this point, I'm a bit skeptical, as the logic and the configuration of the 2 JMeter and Gatling are quite different, so the features and the way to use them don't map 1:1.
The easiest way to work with REST APIs is to use the recorder, so you'd dump request bodies as template and then inject data into them. See http://gatling.io/docs/2.1.6/http/http_request.html#request-body
If you work with JSON, you can use our JsonPath (or standard regex) checks in order to make assertions on the response body, or even capture data. See http://gatling.io/docs/2.1.6/http/http_check.html#defining-the-check-type