For another, that they have large fancy offices in prime locations, with many staff (Huobi had 50, IIRC). Either Huobi or OKCoin moved to larger offices some months ago.
Finally, they are indeed well-funded, but why would anyone invest in them (10 million US$ just in one of them, IIRC) if they were not profitable?
There are many laws that strictly forbid operators of ordinary stock exchanges from profiting by exploiting their privileged position -- namely, their knowledge of the order book before it is posted to the public -- to trade against their clients. Those laws do not apply to bitcoin exchanges. Why would the owners not do those things, if they are legal for them?
The fact that they have offices in prime locations with a lot of staff could mean they are well funded.
I would find it plausible that Chinese exchanges were trading using their own funds for profit and were making a lot of money. I would also say that this practice can be extremely risky and would make holding funds at these exchanges risky as well.