First of all if you haven't downloaded RED Groups then I recommend you do, as it contains some pre made objects that can be used. I'm not sure if the object you're looking for was already placed in your RED Editor but I'm not taking the risk.
There's a object that goes under Clutter/ Natural/ Plants in Object Mode and it goes under the name 'danglingplant1'. This is essentially grass hanging upside down, all you need to do is rorate it the other way round and you've got grass that you can walk through.
P.s. In the editor one side of the grass face may not render in the Editor but renders when you play it in the game. Have fun.