diff --git a/tests/entrypoints/test_async_omni_diffusion_config.py b/tests/entrypoints/test_async_omni_diffusion_config.py
index 83b465fdb47..063e06094b8 100644
--- a/tests/entrypoints/test_async_omni_diffusion_config.py
+++ b/tests/entrypoints/test_async_omni_diffusion_config.py
@@ -121,6 +121,46 @@ def test_default_stage_config_includes_default_sampling_params():
     }
 
 
+def test_default_stage_config_engine_args():
+    """Ensure default diffusion-stage builder sets and propagates engine_args."""
+    stage_cfg = AsyncOmniEngine._create_default_diffusion_stage_cfg(
+        {
+            "distributed_executor_backend": "ray",
+            "boundary_ratio": 0.875,
+            "flow_shift": 5.0,
+            "trust_remote_code": True,
+        }
+    )[0]
+
+    engine_args = stage_cfg["engine_args"]
+    assert engine_args["distributed_executor_backend"] == "ray"
+    assert engine_args["boundary_ratio"] == 0.875
+    assert engine_args["flow_shift"] == 5.0
+    assert engine_args["trust_remote_code"] is True
+
+
+def test_default_stage_config_whitelist_none_fallback():
+    """DeployConfig / StageDeployConfig whitelist fields with value None
+    fall back to OmniDiffusionConfig dataclass defaults."""
+    stage_cfg = AsyncOmniEngine._create_default_diffusion_stage_cfg(
+        {
+            # DeployConfig pipeline-wide
+            "trust_remote_code": None,
+            "distributed_executor_backend": None,
+            "dtype": None,
+            # StageDeployConfig
+            "enforce_eager": None,
+        }
+    )[0]
+
+    engine_args = stage_cfg["engine_args"]
+
+    assert engine_args["trust_remote_code"] is False
+    assert engine_args["distributed_executor_backend"] == "mp"
+    assert engine_args["dtype"] == "auto"
+    assert engine_args["enforce_eager"] is False
+
+
 def test_serve_cli_accepts_ulysses_mode():
     """Ensure diffusion serve CLI exposes ulysses_mode and wires it to parallel_config."""
     parser = FlexibleArgumentParser()
diff --git a/vllm_omni/engine/async_omni_engine.py b/vllm_omni/engine/async_omni_engine.py
index 66096de7c0c..1483210cdf1 100644
--- a/vllm_omni/engine/async_omni_engine.py
+++ b/vllm_omni/engine/async_omni_engine.py
@@ -1346,6 +1346,10 @@ def _create_default_diffusion_stage_cfg(kwargs: dict[str, Any]) -> list:
             "diffusion_load_format": kwargs.get("diffusion_load_format", "default"),
             "custom_pipeline_args": kwargs.get("custom_pipeline_args", None),
             "worker_extension_cls": kwargs.get("worker_extension_cls", None),
+            "trust_remote_code": (False if kwargs.get("trust_remote_code") is None else kwargs["trust_remote_code"]),
+            "distributed_executor_backend": (
+                "mp" if kwargs.get("distributed_executor_backend") is None else kwargs["distributed_executor_backend"]
+            ),
             "enable_sleep_mode": kwargs.get("enable_sleep_mode", False),
             "enable_multithread_weight_load": kwargs.get("enable_multithread_weight_load", True),
             "num_weight_load_threads": kwargs.get("num_weight_load_threads", 4),