Royal,
There should be no interference as long as you do not implant them in the same place. I am not sure what you have in mind but you tend to find biomagnets in fingertips, behind the hear, or other sensitive areas. while the flex can go anywhere the sites its recommended to be implanted at, are different then the places the magnets would be, accept say the fingertips.
Do you know where you plan to put your bio magnets and the flex tag?