The only time you will impact current systems in production is if your current environment relies on dhcp next-server (option 66) or boot-file (option 67) or uses ProxyDHCP (udp port 4011) to communicate configuration files to your booting devices (such as a voip phone needing to find the pbx system to get its configuration file). If a booting device never attempts to get booting information from dhcp then there is no impact.

Having FOG and either Microsoft’s WDS or SCCM on the same network will cause conflicts.