Microsoft introduced a new feature for subnet failover configuration in Server 2012 R2. This feature basically allows you to create a split scope without sacrificing the IP space you configured on the second server (i.e in a 50/50 scope you can only utilize 50% of your IP's). Solarwinds IPAM should be able to configure and manage these failover scopes just like a split scope.
I have included some Microsoft TechNet articles covering this new feature and some of its configuration options.
DHCP Failover Load Balance Mode - Microsoft Windows DHCP Team Blog - Site Home - TechNet Blogs
DHCP Failover Hot-Standby Mode - Microsoft Windows DHCP Team Blog - Site Home - TechNet Blogs