would depend on the size of the rocks and how established the other rock is....def playing roulette though and def not worth the chance of crashing your other system....theres no harm really if theres no fish or corals.
why not cure the rock first why the rush?? rushing is what kills tanks and patience is the game nothing happens fast in a reeftank but disater..
to cure the rock its quite simple just aquire a rubbermate or large similar bin or even another tank....fill with salt water at 1.025 keep temp around normal using a heater.no light is needed.use a powerhead to maintain flow.change out water frequently as it will smell rancid.keep an eye out for amonia once the amonia is non readable and the smell is gone you can start to safely add small amounts at a time to your established tank.
adding rock that has a really high amonia source is very very sketchy and i def would not recommend it as its sure to briung death to your fish and inverts.adding rock that comes from a low amonia souce or small dieoff is still border line but can be done in small amounts only if the system its going in is established with a low bio load and has a very good quality of lr to quickly covert the amonia.
make a wise choice and cure the rock seperately before doing this trust me been there done that and its not a good idea
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