We prove uniqueness of representations of Nica-Toeplitz algebras associated to product systems of C * -correspondences over right LCM semigroups by applying our previous abstract uniqueness results developed for C * -precategories. Our results provide an interpretation of conditions identified in work of Fowler and Fowler-Raeburn, and apply also to their crossed product twisted by a product system, in the new context of right LCM semigroups, as well as to a new, Doplicher-Roberts type C * -algebra associated to the Nica-Toeplitz algebra. As a derived construction we develop Nica-Toeplitz crossed products by actions with completely positive maps. This provides a unified framework for Nica-Toeplitz semigroup crossed products by endomorphisms and by transfer operators. We illustrate these two classes of examples with semigroup C * -algebras of right and left semidirect products. A x, y · z = x · y, z A for all x, y, z ∈ X. An equivalence A-bimodule is a Hilbert bimodule which is full over left and right. We say that two Hilbert A-bimodules X, Y are Morita equivalent if there is an equivalence A-bimodule E such that X ⊗ A E ∼ = Y ⊗ A E. Remark 1.3. A product system X is (left) essential if each C