This addresses one of my concerns about using the music for routines, but not the other: I often (in fact, almost always) have to modify tracks to make them work as floor routine music, which goes explicitly against part C of the terms of use.
I have always asked the ReMixers before using their ReMixes as routine music. Does this constitute getting a separate license from the remixer? If so, then don't worry about changing the terms of use just to accomodate me; I can just continue to use remixes with permission (ie licenses) obtained directly from the arranger.
IF we go by the assumption that I am using it under an independant license from the remixer, it raises another issue: should/could I still attribute the track to OCR if anybody asks? I would be using a modified version of the mix under a different license from the one offered by the site; though it would not be explicitly against the terms of use for me to attribute it to OCR, it seems it would be a violation of the submission agreement for the arranger to give me permission to do so.