Here's a small pastel painting on Uart grade 240 paper, which is the roughest of all the Uart grades.
Certainly eats the pastels, but you get some good rich colouring as the paper grabs the pastel in greater amounts. I've just got trial/sample sheets at the moment but hope to order some fullsize sheets very soon. There is a wavy type of "grain" to the paper which becomes visible as soon as pastel goes onto the surface; but it is not unpleasant and I expect to find various ways of coping with it. The paper itself is a kind of grey-beige colour and will accept wet media, so there's plenty of opportunity to experiment with wet underpaintings.