Can salad dressing be made with coconut oil?
Yes, you can, but it needs to be a warm dressing.

The only warm dressing that I'm aware of is for spinach salad, where you use bacon fat to make the dressing.  See Alton Brown's Spinach Salad with Warm Bacon Dressing

I would stick with dark, hearty greens or cabbage, as they'll hold up better to the heat than most lettuces will.