Gotta love clearance plants! Whenever I go to Lowe's, I always make a point to check out the clearance section of the garden center.
Personally, I have never had issues growing mums with other plants. I have them in various beds across the property and they seem to get along with whatever is growing near them. I also use them in mixed container plantings I sell at the markets each fall, and they're usually packed in there tight enough that they share the same root zone with the other plants in the container.