Dive-planes (at least those in WW2 fashion) are an important tool to keep the sub level in the water. While you could of course do that too with trim tanks it's not a wise thing to do as pumps make a lot more noise than the hydraulic movement of the dive-planes. If you set the dive-planes to rise together with speed of the screw the hydrodynamic capabilities of the dive-planes will give you a lift but the buoyancy caused by the water in the ballast-tanks will drag the sub back down. So yes, it's possible to stall a sub.
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