You can't get the hash values from NiceHash because if you have more than one miner running you are seeing cumulative values rather than for one miner. Also, the accept/reject rates jump around a lot and are not reliable gauges of actual speed.
The hash rate Nicehash reports is the important one, as that is what generates the payment. Yes, it jumps around a lot, but that is what the running average is for. Also, nowadays Nicehash supports workers and reports their hashrate.
Edit: I'm running a script to test the averaging at the moment. Give me a couple of hours to get some results.
I'll be curious to see your results.
I haven't checked lately, but I don't think the NiceHash API has a method for getting per worker stats yet. That will be needed in order to bring it into NHC.