I doubt a leopard tortoise will eat pampas grass. The edges of the leaves are very rough. But he will appreciate the opportunity to hide under it. Pampas grass is great for hiding under.
I agree with Yvonne. Doubt they eat it but I know they would love to hide under it. Mine don't really eat decorative grasses like monkey grass and stuff, but they do love to climb under the clumps and hide, usually with their little head sticking out of the pile.