Please keep this in mind:
Aluminum is not ferromagnetic.
We actually considered using an electromagnet to attach to the *aluminum* diamond plating. Yeah...that's what happens when the programmers start thinking about anything but programming...
I don't see any rule that states anything against using an electromagnet. I don't think that a weak magnetic force would have any negative effects on the robot controller; just don't wave it around in close proximity just to see what happens.
I don't know how much such a magnet would draw; you might research this yourself. You do need to make sure it complies with all the rules, and you also need to ensure that the entire device can easily be removed for inspection. The inspectors probably haven't seen many devices similar to what you propose, so they will definitely want a closer look.
Remember the KISS rule (keep it simple stupid)--don't go all-out with an electromagnet when a pneumatic will do.
Good luck,
JBot