I've used pre-slotted Stew-Mac boards as well as my own boards, slotted with a Stew-Mac saw, fretted with Stew-Mac fretwire and what I noticed is that with harder woods like Ebony, I almost always end up having some amount of back bow after fretting. I let the neck rest a little after fretting and apply some moderate pressure in the middle of the neck to let things settle. After a couple of days, the amount of bow lessens and sometimes dissapears. The amount of variance depends on the neck stiffness. For example, a 1/4 saw piece of maple with have more resistance to back bow, as will a laminated piece. I've used maple a couple of times with Wenge and had no issues.
The thing is, anything you do on the neck will affect its straightness. I try to start with something that is a flat as possible but there are always some adjustments to do after fretting with hard words. Rosewood isn't as bad as Ebony.