Indeed, they are. Well, Bitcoin.com belongs to Roger so Roger = Jihan = Bitmain.
Not just that. Bitcoin.com announced that they will use 2x chain as a main chain, they will literally ignore the legacy chain.
You shouldn't listen to nor take anything that Roger Ver says seriously. He's a spoiled manchild. He recently said that Bitcoin Cash is the true Bitcoin, then change his statement to 2x a few days after. His statements are worthless, nor is he or this band of suits able to define Bitcoin.
I also think that Roger's manchild nature is probably keeping him from listening to good legal counsel on this. If Bitcoin.com really ignores the legacy chain, changes the "BTC" ticker to an altcoin, and pawns these off on buyers / wallet users, Roger is in for a world of hurt when the lawsuits start rolling in. Bitcoin.com is brokering the exchange of goods and as a custodian, there are certain duties of care that must be taken from a legal perspective.
Bixin also supports Segwit2x from the beginning.
That does not necessarily have to imply that they are a Bitmain proxy (and I sure hope that they are not). There's still time for them to pull out of the agreement.
Bixin's policy towards Bitcoin Cash suggests that they are not a Bitmain proxy. But I suppose that could be a red herring.