underscore character in domain name

I started work with a company that has an underscore character in their domain name. The network is strictly private our email is hosted outside and uses a different domain name.

I want to decomission two old NT servers and go to all 2000 servers and AD. I have 250 machines and am hoping I don’t need to change the domain name. Can I leave the domain name as is?

Any help would be appreciated.

Thanks
flyersix