Although leather's may not particularly like high flow, they certainly need good flow. They need the flow in order to shed their mucous layer and to get
detritus off of their surface. Also, the leather may react for awhile to the clown by closing its polyps up. Give it some time to adjust to the clown rolling around on it. But, keep your eye on it. If the clown doesn't ever let it open up its polyps, they you may have to go with something else. Typically it's not a problem though....
can't wait to see how it works out for you!
btw...my two clown pairs host a Euphyllia paradivisa and a green/brown zoo colony.