This article develops and evaluates state-dependent parameter (SDP) control systems for the hydraulically actuated dual-manipulators of a mobile nuclear decommissioning robot. A unified framework for calibration and SDP model identification is proposed, in which the state-dependent variable is a delayed voltage input associated with the time-varying system gain. Such nonlinearities can cause undesirable joint movements under automatic control. Hence, the present article develops a nonlinear pole assignment algorithm for the SDP model. Closed-loop experimental data shows that the SDP design more closely follows the joint angle commands than an equivalent linear algorithm, offering improved resolved motion.