You're generally forced to do OLCI with the operating carrier, so even if you start the process on the AF site, it should take you to DL.dumb. Since you're flying ex-EU, you'll be protected under the EU regulations in the case of delays and compensation regardless of whom you check in with. However, you'll probably have to fight DL for compensation harder than you would AF, since DL is only subject to the regulations when operating flights out of the EU.