Connection of SIMATIC components with Allen-Bradley/Rockwell components
Although the documents are prior to the development of the S7-1200, I believe they are still a very good indication of the access possibilities.
As far as Ethernet is concerned Siemens (Industrial Ethernet / Profinet) and Rockwell (Ethernet/IP) are not compatible, and a gateway would be necessary, either the Echochange Ethernet gateway or the Ethernet/IP (or DeviceNet)to Profibus gateways described.
In all the projects where I have to echange data between the S7 and the Logix family I have always found Profibus-DP easy to install and configure. On the Rockwell side you could look at the Prosoft or the SST (now Molex) DP master or slave cards, they are robust and have all the required program blocks for setup. Of course you would need Profibus connectivity on the S7-1299 side also.
SST™ PB3 Remote Modules for PROFIBUS - Molex

PROFIBUS Solutions - ProSoft Technology
Hope this helps,
Daniel Chartier