Can diplopia rule you out if considering lasik?

Technically no: But wouldn't you want to fix your dipolopia before cutting on your cornea? In fact having sharper vision may worsen your diplopia.

Diplopia and LASIK: I have treated about 100 patients with amblyopia, strabismus, and diplopia with lasek and presented the largest series in the world like this at escrs in milan in 2012. Basically, you need to refer to a pediatric ophthalmologist first to make sure the better vision after lasek will help straighten the eyes, or get strabismus surgery first, so you don't get two clear double images, which is worse.

Possibly: If it is not corrected with a glasses or contact lens prescription, then it needs to be evaluated and treated prior to lasik surgery.