No problems .
1.) Created a UMG Widget and put a button in it.
2.) Created a Slate Widget Style using Button as the template
3.) Assigned some textures and settings to the Normal, Pressed, etc… in the Slate Widget Style I created in step 2
4.) Assigned that Slate Widget Style to the button I created in step 1.
Did on the 4.4.0 from the launcher.