I am no expert in the matter but one problem that I would have with it would perhaps be the introduction of either foreign bacteria in your tank or foreign chemicals. Antlers are quite porous I'd assume and thus spending time outside would cause the antlers to accumulate strange bacterial spores that I'm sure aren't common in fish tanks which may cause problems. The second thing I could think of would be how antlers would weather in salt water for any long period of time. And I wouldn't even think about laquering them before putting them in the tank either.