I use muscle relaxants with LMAs all of the time and I am criticized for doing so, although when I ask the critics why I should not, they have no data to support their criticism.
I believe LMAs actually work better when the patient is relaxed. Light anesthesia and poor relaxation contribute to LMA malfunction.
This link will bring you to a pdf taken from the LMA of North America website that supports my position on this:
Detractors are encouraged to leave a comment to this post.