If the decoration is just pure wood, yes, it's safe. Reptile logs are heat treated though, so they usually will take a LOT of boiling and or general soaking to get waterlogged enough to sink. I had to boil one of the Petsmart reptile driftwoods on and off for 3 days straight, and even then it still took couple days to finally stay sunk without being weighted down. You'll also tend to get bacteria bloom in the form of a clear slime that can be unsightly, but it goes away within a week or so. Some snails, shrimp, and fish may eat the slime, but if not it can be scrubbed off pretty easily.