Doppler radars have potential for accurate structural displacement measurements by transmitting radio frequency (RF) waves that are phase-modulated by the motion of a vibrating target. Existing works have considered the use of active and passive tags to improve the measurement accuracy by either increasing the signal to noise ratio of the received signal or by doubling the frequency of the returned signal. However, structural displacement estimation using Doppler radars in scenarios with strong interferences has not been reported. In this paper, the feasibility of using Doppler radars assisted by active RF tags to estimate structural displacement when multiple moving objects are also illuminated by the same sensor is investigated. Leveraging an active tag, the signal associated with the structural vibration is upconverted to allow easy frequency discrimination for the signal of interest. By applying a digital filtering-based approach, interference rejection is achieved, and an accurate tag-referenced displacement can be retrieved.