Yes, because the D500 has no built-in flash. Otherwise the SB-700 could be triggered via the internal flash, i.e. the SB-700 waits until the D500 flashes and then flashes. As far as I know, this is triggered in such a way that the first "trigger" flash has hardly any influence on the photo.
But a transmitter works more reliably in any case. The triggering with the internal flash described above does not always work for me.