Can the CSR key be generated using Microsoft Server IIS instead of OpenSSL for the Custom Secure Domain?

Since NetSuite is using APACHE, it is recommended to use OpenSSL. There are other tools like Ensim that can be used, but OpenSSL is the easiest and most inexpensive way.

In addition, if you use Microsoft Server (IIS) to generate the CSR key, the encryption might be specific only to Microsoft.