Can I configure DHCP split scope using our current Windows 2008 server with DHCP, and a new Windows 2012 server which I have installed DHCP on?
Yes, it is possible. Really the 2 servers don't share info in a split scope setup so if you manually configure each scope (80/20 or whatever) then sure, it will work.
However, if you have the ability to make both DHCP servers 2012 servers that would allow you to use Failover instead. A better option that allows for load balancing and replication of scope information/leases between the 2.
But yeah, basically you can run a 2008 DHCP server and a 2012 DHCP server in a split scope. Technically you could run a 2012 DHCP server and a Linux DHCP server in split scope if you wanted to.