As it stands right now, ReadyAPI does have the support for the Selenium Webdriver and it does work to some extent.
There is a way to build a reusable code by adding Groovy functions for the project by dropping the files in the /ext folder.
Overall, the Selenium framework is much more complex and it has POM (page object model), data sources, and other things that make up a true, full-fledged framework.
We need to have a ReadyAPI support to implement it as well as support the debugging capabilities/ IDE for it.