The dimension style "comes from a block"? That confuses me. And it's doing things the hard way as well. Why not open both drawings and drag the dimstyle from the block drawing directly into the new drawing?
But allow me to ask a more basic question: Do you have a standard template file containing layers, scales, text, dimension, mleader, table styles, and title blocks? If not, you should. Doing so would make your day so much more efficient.
Dave Hein, P.E.
I know you said you deleted and purged, but it sounds like there was already a dimension style with that name in the drawing, therefore the imported Dimstyle inherited the properties of the existing dimstyle. The same thing would happen dragging from Design Center however you do have the right-click option(s) to "Redefine"
Can you confirm that those dimstyle names do no exist in the drawing prior to inserting the block?