I've got one of their Rough Mats (the ones without turf) and one of the Surf Mats (water ones).
They are made of a kind of canvass, painted and with texturing (think flocking and gravel).
For the rocks, there should be no problem at all.
For the trees, I am not sure how stable the base is. They surely can be placed on, and I don't think there should be much difference from a normal flat mat, maybe you can't place them just everywhere, but maybe you'll need to move their placement 1 cm from where you wanted them, if that exact spot has too rough texturing.
I will try and take a picture with something on, just soonish, I can't today...