Integrated sensing and communication (ISAC) enables communication and sensing to share wireless resources, but sensing performance can degrade when strong environmental reflections and coexistence effects obscure weak target responses. This paper investigates a hybrid orthogonal frequency-division multiplexing (OFDM) and orthogonal time frequency space (OTFS) architecture in which an OFDM region supports communication and provides pilot observations for estimating the static environmental channel, while an adjacent OTFS region performs delay-Doppler sensing. A finite delay-dictionary least-squares estimator reconstructs the static channel over the OTFS band, followed by time-frequency-domain cancellation before delay-Doppler processing. The proposed architecture is evaluated against a full-band 256-subcarrier OTFS baseline and an uncancelled hybrid configuration using a common sensing framework. The estimator achieves approximately 19 to 20 dB normalized mean-squared error (NMSE) across the evaluated clutter-to-noise ratio (CNR) range, while the proposed cancellation improves the target-to-clutter ratio by up to 30.7 dB over the uncancelled hybrid case at high CNR. A dedicated low-Doppler experiment further demonstrates improved detection in the presence of near-zero-Doppler clutter. The hybrid architecture incurs a four-times coarser nominal range resolution and a 5.88 dB OTFS processing-gain penalty while allocating 71.9% of the subcarriers to OFDM. Fixed-point results show that 16-bit Q5.10 arithmetic closely tracks floating-point channel estimation, supporting hardware-aware implementation.

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