If a mech unit with rumble scrapper gets coppied does the rumble scrapper effect adds another +2

Yes — if the copied unit is Rumble, Scrapper himself. Copy effects copy his rules text and tags (Rule 477.1.b.1.a), so a Reflection/Mirror Image copy is a second Rumble with his own static "Your Mechs have +1 [M] (including me)" ability, and two separate sources stack: your Mechs get +2 total, and each Rumble gets +1 from both abilities (6 Might).

If instead you meant copying some other Mech while Rumble is on the board: no +2. The copy comes in at its printed Might — copy effects don't include bonuses granted by other cards — and then Rumble's effect applies exactly once, giving it the same +1 every other Mech gets.