Official comment
That's just the OS telling you that one of the portions of the application is not 64bit (it's one of the networking modules). Currently, legacy 32bit modules and applications can continue to operate, but in an effort to provide a more secure computing environment, Apple decided to start warning users as the next version of the OS will likely block them completely.
Pioneer DJ is aware of this and will have it updated in a future release. For the time being, there's no need to worry.