Actually you made me curious, so I made some tests.
NVR: DS-7608NI-E2/8P/A, latest FW V3.3.4
I connected the following cameras on the PoE ports:
1. Vivotek IP7161. Result: Powered up normally, was able to get only the main stream working under Vivotek protocol.
2. CNB MGC6050F. Result: Powered up normally, was able to get the both streams working OK under ONVIF protocol.
So for me, it seems that integrated PoE ports works as 802.3af fully compatible.