Cautiously. Since nair is primarily external and is not absorbed in the skin it is likely safe. That being said skin changes are common during pregnancy and creams, lotions, deodorants, etc that were well tolerated before can sometimes cause unexpected rashes before. Nair can be very irritating to skin for many, so use caution. Also avoid using it in the genital region.
Every doctor I know. says it is fine. I guess I am coming from a different angle. If it is left on too long,used in an inappropriate area or if your skin in sensitive it could lead to rash, sometimes blistering. My general philosophy is not use any unnecessary chemicals/ substances during pregnancy. Please be aware that most providers I know might think that my views are on the "cautious" side.