BuyBuyBaby - yes, but not expired ones like they will take at Bed Bath & Beyond (BUMMER!). There is a list of brands that are excluded from the coupons written right on the coupon, and it includes baby items (like Peg Perego). If Mamaroo isn't on there, I would say you should be fine.
Babies R Us - I don't know, I never tried.
It depends on the BRU. If it is near a BBB, they will sometimes take Bed bath and beyond coupons as long as they are not expired. The BRU near me takes the coupons.
Also, Buy Buy Baby will accept BRU coupons too as long as they are not expired. BBB will also take Baby Depot coupons too.