I'm using Server Manager on Win 8.1 Update and have DHCP installed and running on a Server Core 2012 R2 domain controller. The BPA believes Option 3 (Default Gateway/Router) is not set. But it actually is set. It's set in the Server Options and appears in the Scope Options.
I've also confirmed that DHCP clients have the Default Gateway set properly so I know it's working as expected. I've even deleted and recreated the option but BPA still believes it's not set.
I could exclude this check from the BPA but I'd rather get to the bottom of it and correct whatever the issue is.
Consider what would happen when you add a second scope-vlan for another network that is getting to this DHCP server via a DHCP relay. The default gateway you have provided as a server wide option would typically not be valid on the second scope.
The default gateway is usually something that is strongly tied to a specific scope, and not a particular DHCP server. A scope defines information for a particular subnet.
Does a default gateway really make sense in the server options? I don't think it does, and I am not too surprised that a BPA would flag this as unusual.