Strategic ops page 85 says: "...High Speed Closing Engagements address this in part, recognizing the influence on damage for ballistic and missile weapons. Energy weapons ... are not affected by closing velocity." Based on this, you might think that machine guns (as direct fire ballistic weapons) have damage multiplied in a high speed closing engagement.
However, in the next paragraph it says: "...the damage by missile, autocannon, and Gauss weaponry is multiplied by 1.5..." Machine guns fit none of these categories.
And Giovanni adds from the paragraph after: "... it would be awkward for a battleship to be destroyed by a machine gun..." again implying that machine guns should have damage increased.
So, should machine gun fire have a damage multiplier when used in a high speed engagement?