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

Yes — a copy of Rumble, Scrapper stacks with the original, so your Mechs get +2 Might total. Just to be precise: the bonus is +1 per Rumble, not +2 per copy.

Copy effects copy the copyable traits of the original — Name, Type, Tags, and Rules Text (Rule 477.1.b.1.a) — so the Reflection/Deceiver copy is itself a Mech with the same passive "Your Mechs have +1 Might (including me)." Passive abilities from two different sources both apply in the Arithmetic layer, and there's no rule preventing identical statics from stacking — same as if you controlled two real copies of Rumble, Scrapper. The same logic also means a copy of any regular Mech is still a Mech, so it picks up Rumble's +1 even if it enters after he's on the board.