I too have heard about the keeper being a no-no with the IUD, so I asked my gyn, and he told me that it was really hard to remove an IUD, and that succion alone could not get it out, so it wasn't a concern.
edited to add that I have used my keeper a few times with my IUD, with no problems, but since it is a MIRENA (hormonal), I haven't had periods in over a year, so I haven't had the chance to use it much...