I think I read somewhere that Bitmain probably made more then Nvidia last year.
Rumored, but no HARD numbers are available for Bitmain.
Given they probably have a lot higher margin on their sales, their profits being higher than Nvidia in 2017 would be no shock.
I think Bitmain is buying the chips from TSMC so they are probably getting good deals on those and I would assume they have higher profits that Nvidia does.