Q. If I have users in a China or Germany Azure AD be integrated with a Global Azure AD instance?

A. Both China and Germany Azure regions are separate, isolated entities (for sovereignty reasons) and the Azure AD instances also isolated. This means users from a Germany or China based Azure AD instance cannot be granted access to a global Azure resource including access to a global Azure AD. It also applies the opposite direction, a global Azure AD user cannot be granted access to a Germany or China based Azure resource.