What kind of random numbers source does getnewaddress in Bitcoin Core API (bitcoind) uses?
As others mentioned Bitcoin core uses OpenSSL random sources.

This means that it uses any random source available, like:


the operation system, i.e. interrupts
random sources of the CPU or the chip set
dedicated hardware for entropy generation


So in order to make sure your hardware random generator works with Bitcoin you must make sure it works with OpenSSL.