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

No — a copy doesn't stack Rumble's bonus. Copy effects only copy copyable traits (printed Name, Type, Tags, Cost, Domain, Rules Text — Rule 477.1.b.1.a), so a copied Mech enters at its printed Might; the +1 from Rumble, Scrapper is a passive granted by a separate permanent, not a trait of the unit, so it isn't copied. The copy is still a Mech, so Rumble's passive applies to it once like any other Mech — the copy ends up at the same Might as the original, not +2.

If you meant copying Rumble, Scrapper himself, then yes: his Rules Text is copyable, so the copy also says "Your Mechs have +1 [M] (including me)," and with both in play your Mechs get +2 total.