I have no trouble with wooden molds in the oven, as I CPOP frequently. Pre-warming in the oven is fine. As a precaution, just pre-heat the oven, then put the wooden mold on top of an oven-safe tray of some kind with a towel or parchment paper or a towel to protect the tray from anything on the wood (old soap, glue, etc.). Before you put the mold into the oven, TURN IT OFF, then put the mold in the pre-heated oven.
I emphasize turning off the oven as a precaution to make sure to develop a habit that will prevent you from accidentally forgetting about it and cooking your mold for some extended period of time. It's too easy to get distracted and forget about it. Why take that risk?
What @earlene said.
I also recommended either taping a note or using a sticky note over the oven controls that's says there is soap in there. Otherwise, somebody* could forget about the soap and turn the oven on for a pizza or something and ruin your soap and make a mess.
Do you mean keeping your molds warm, as in to keep your batter fluid while you pour?
If so, it might help a bit if you can figure out how but it's not absolutely necessary especially if everything else is warm.
I think once the soap is in there it will hold heat better than when you're pouring it between containers or mixing in colorants, coz the heat can escape while doing those, so the containers are what you should be heating, if you need to.
Unless you're doing single colored soaps. I find I don't really need to heat up anything with those, only when I want to try a swirl technique.