Safe is a relative term, and the answer may depend on a host of factors that vary tank to tank and species to species.
I choose vinegar instead of vodka, but I know that at high doses I can turn RBTAs brownish with excessive zoox, as presumably the zoox thrive on the acetate. The same may happen with vodka, but I've not specifically heard of that. At lower doses, such changes did not occur. I currently dose vinegar and keep giganteas.
That said, there have been some reports of issues with organic carbon dosing and anemones, including my own large H. crispa. Was it coincidence, or cause and effect? Not sure. But one can hypothesize that anemones struggling against bacterial infections may be harmed by added organic carbon sources which may help spur bacterial growth.