The motion of cellulose whiskers trapped in agarose hydrogels is measured by depolarized dynamic light scattering (DDLS) under conditions of optical heterodyning, in which the rigid polymer network provides a static depolarized reference signal. At low concentration in free suspension, the rotational relaxation rate Theta of the whiskers is decoupled from the osmotic properties of the suspension. When incorporated inside a gel, however, as the agarose concentration increases, Theta first increases beyond that in the free suspension, reflecting a reduced amplitude of rotational fluctuations of the whiskers due to the repulsive interactions with their surroundings. At the same time, the dynamic light scattering Rayleigh ratio R-VH obtained from DDLS decreases with increasing gel concentration. At high gel concentrations, however, Theta tends to decrease due to the steric hindrance of the network. Except at the lowest whisker concentrations, Theta is governed by the same fluctuations as those associated with R-VH.