DOM is DRAWN OVER MANDREL so there is no seam line inside of the tubing. EWS is just standard mild steel tubing the only advantage of the DOM is the more exact Inner diameter. DOM is more expensive than EWS.
I Personally would give S&W call and ask them.
Since your roll cage will be ultra sonic thickness tested, I would consider going up one wall thickness size from the minimum required.
Tubing as manufactured has a tolerance .120 wall tubing may be .118-.122 an it can get even thinner on the outside of a bend.
While slightly thicker tubing is a little heavyer it can be a huge PITA to change out a tube in a completed roll cage.
