I don't have a lot of experience with keeping a tank, my last one was a few years ago, but I would be concerned about the wood rotting. Also I think the resins found in coniferous woods can actually harm fish, so probably better watch that.
Hmm, I'm guessing that since it was used for a lizard the bit of wood is also dry, with any wood you use in the tank it would probably be best for it to be waterlogged, I've heard that boiling the wood can speed up that process and also kills off any bacteria that may be living in the wood. And even if the wood was hardwood and waterlogged, or became waterlogged, I think it would still rot to some extent which still posses a risk to your betta.
If your end goal is simply to have a bit of wood in a tank for a more natural feel then I think it may be best to simply get some driftwood from a freshwater source...
Anyways good luck with whatever you decide!