I think it would be appropriate to explain up-front that the film might contaminate a C-41 process, especially if a lot of film runs through. I used to work at a pro lab, and the continuous testing and calibration of the various processes was painstaking, and I remember every time some cross processing came in there would be frowning faces among those that operated film processing.
Cross processing is cool. We have all seen the work of JD Callow on this web site, for instance. His X-processed images are just phenomenal, and the creative possibilities are exciting to say the least.
It's cool that Rollei has come out with these films, probably to satisfy the lo-fi types of photographers. But it would have been even cooler if there was a disclaimer about the cross processing. You may also want to invest some time in recommending to process these at home with a C-41 processing kit. They work quite well, are fairly inexpensive, and are a lot easier to do than most people imagine.