Yes, you can put the baby on your wife's insurance, even if you're planning to switch them both to your insurance later. Should you? It depends. Would your wife's deductible and out-of-pocket max increase if the plan covered two people instead of just herself? That might cause less of the delivery to be covered if so. You'll have to balance that against the extra costs that would be paid by adding the baby to your plan if you have used little/none of your own deductible yet this year.
Sometimes covering the mom and/or baby on both insurance plans can be the optimal choice. Check out the "coordination of benefits" provisions in your respective plans to get info about this. My wife and I double-enrolled her for both times she gave birth, starting from the date of the birth. My plan ended up paying a very large chunk of what her out-of-pocket costs would have been if she had only been covered by one insurance, and all it cost us was a bit higher premiums for the rest of the year after each kid was born.
