Ultimate Grass & Meadows appears to use instancing, so chances are your are not seeing any preview as you are looking at are instances with their preview set to bounding box. There are numerous ways to overcome this with the easiest likely to be post. Simply render your seen with and without the grass and composite the two together using an image manipulation program. The next method relies on replacing the instances with actual geometry and using one of the above described methods such as Dformers or mesh grabbers to push and pull the actual geometry so collision with your figure is minimised. Hope this helps :)