FusionAuth Cloud instances may or may not have static egress IP addresses; please open a support ticket with your instance name to learn more.

VPC peering is not currently supported, though that issue is the right one to follow for future developments.

You can also use an LDAP proxy to solve this issue.

FusionAuth -> LDAP proxy -> AD

where the LDAP proxy is in the DMZ and AD is configured to only talk to internal network values or the LDAP proxy.

Here's a StackOverflow post with more details.