I don't know if it's a problem. I had someone mention to me just a few weeks ago that the hooks are not listed to be used with mc.
What I have found is the cat hooks are under the U.L. file number E165703 which can be found here:
http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073985904&sequence=1
Under General Information for Conduit and Cable Hardware is the following
"The following, where applicable, is marked on the carton or installation instructions provided on or in the carton:
1. Types or range of thicknesses of a beam flange, drop wire, or rod
2. Intended mounting orientations, if restricted (for example, vertical or horizontal)
3. Sizes and types of conduit, cable, or tubing intended to be supported for hangers, staples, and straps
4. Load rating greater than for the intended applications
5. Designated assembly torque when other than intended
"
According to number 3, the carton that the hooks come in or the installation directions must list the types of conduit and cables intended to be supported.
I don't have a box of cat hooks near me, but I can't remember ever reading anything on the box or in the directions about use with mc.
I only remember reading the number of data cables the individual hooks can support.